Here is critical information you need to know for a tactical advantage as a Spectre agent:

Combat

1. You lose accuracy as you fire your weapon. Fire in controlled bursts for maximum effect.
2. Use Zoom (L-trigger) to improve your accuracy during combat.
3. Put points into the First Aid skill to increase the amount of health regained from each medigel use.
4. Your targeting reticle will autolock on nearby enemies. It will change color once it is locked on. Your attacks will aim at autolocked targets even if your reticle isn't focused on them.
5. Toxic damage reduces the amount of health you regain from Medi-gel.
6. STORMING automatically performs a melee attack against any enemy you run into. Be sure to watch the meter at the bottom left of the screen, though, to avoid becoming fatigued.
7. Throwing a Grenade beside an enemy in cover can be brutally effective.  
8. Don't stay in cover too long; many enemies will charge your position
9. Equip each member of your squad with weapons they are trained to use.  
10. Firing from a crouched position improves accuracy.
11. Press R-trigger to rifle-butt enemies at close range. But be careful, enemies can do the same to you, and some of them are far stronger than humans!
12. Use the Power Wheel to set up combos for your squad. Have one squad member Lift a target while another one uses Throw to hurl your enemy across the room.
13. If you use a weapon you are not trained for you will be very inaccurate. Remember to use the L-bumper to bring up the Weapon Wheel if you want to switch weapons.

Squad

1. The squad screen lets you spend talent points to improve your skill with weapons, tech, and biotics.
2. Press UP on the D-pad to send your squad forward to a targeted location.
3. Press DOWN on the D-pad to have your squad hold position and seek cover.
4. Press LEFT on the D-pad to rally your squad and have them regroup around you.
5. Press RIGHT on the D-pad to have your squad attack the highlighted target.

Dialogue

1. Replies on the right side of the conversation wheel generally progress you towards the end of a dialog.
2. Replies on the left side of the conversation wheel will often let you learn additional information from the speaker.
3. Replies on the bottom half of the conversation wheel tend to be more confrontational, and will sometimes earn you Renegade points.
4. Replies on the top half of the conversation wheel tend to be more agreeable, and will sometimes earn you Paragon points.
5. Spending points in Charm or Intimidate will open up new dialog options. Selecting these can earn you Paragon or Renegade points.
6. Press X to skip immediately to the next line of dialog during a conversation.
7. Press A to cue up your responses during dialog. You will reply as soon as the other person finishes talking.
8. Selecting a reply and pressing X will make Shepard respond immediately, cutting off the dialog of the other speaker.
9. A high Renegade score will open up new slots in your Intimidate skill.
10. A high Paragon score will open up new slots in your Charm skill.  
11. Persuade options will be grayed out if you don't have a high enough skill rank in Charm or Intimidate.

Vehicle

1. The Mako can evade incoming rockets using its jump jets.
2. The Mako has two weapons: a heavy artillery cannon (R-Shoulder) as well as an automatic chain gun (R-Trigger).
3. In the Mako you can look through the turret scope by holding the Left Trigger, and zoom in by clicking in the Right Analogue Stick.
4. You can use your Repair skill to fix the Mako.
5. Drive diagonally up steep slopes in the mako, using switchback turns to traverse difficult terrain.
6. While driving the mako, press Y to repair any damage it may have sustained. This uses omnigel.
7. You can revive dead team members by getting back into the Mako.

• Overkill allows long bursts of fire from your assault rifle that can deal an incredible amount of damage to your target
• The increased accuracy Marksman provides to your pistol allows it to be used effectively at long range.
• Carnage does a great deal of damage, and can hurt multiple enemies if they are standing too close together.
• Assassination greatly increases the damage of your sniper rifle, making it the fastest way to take down tough targets.
• Adrenaline Burst immediately restores all your other talents, and is best used when they have all been depleted.
• Immunity provides great protection against all damage types, and can give you time to heal yourself, reach new cover, or charge in close to the enemy
• Normally your shields will not regenerate while under fire, but Shield Boost will quickly restore them in any situation.
• Unity requires medi-gel for use, but it can revive fallen squad mates in the middle of battle to quickly turn the tide against the enemy.
• The First Aid and Medicine talents of all your squad members are pooled together to increase the effectiveness of your First Aid button (Y).
• Neural Shock knocks enemies out, leaving them vulnerable on the floor for several seconds while they recover. Unfortunately it is useless against artificial enemies like Geth and drones.
• AI Hacking will turn an artificial enemy against its squad mates, often causing damage to both the hacked enemy and the ones it attacks.
• An artificial enemy that has been Hacked can still be shot and damaged if you wish, but will not automatically be attacked by your squad mates.
• Damping, Sabotage, and Overload are virtual proximity mines that will detonate when enemies are nearby, but have no effect on friendly units. The radius and damage of their explosions can be increased through talents.
• The Overload mine does extra damage to the shields of enemies caught in the blast, and reduces the effectiveness of their armor for a few seconds as well.
• Sabotage disables special weapon attacks like Carnage, sniper beams, and rockets in addition to disabling normal gunfire.
• Sabotage has no effect on enemies that attack with natural weapons, like the Verran or Rachni.
• The Damping mine disables enemy tech and biotic powers, and may stun enemies for a few seconds as well so they do not move or attack.
• Using Throw against a target that has already been Lifted can have very impressive results.
• Lift picks up enemies, hampering their ability to fight, taking them out of cover, and eventually dropping them for damage.
• Stasis can take a single enemy out of the fight for quite some time, allowing you to concentrate on killing his companions.
• Barrier makes you nearly immune to gunfire, but it provides no protection against attacks that penetrate shields, such as melee strikes.
• Warp does little damage on its own, but if you attack a Warped target you will do far more damage than usual.
• Singularity hits many enemies at once, and often leaves them wounded and close together, allowing follow-up powers to have devastating results on them all.

Creatures

• Have advanced shielding that makes them strong against gunfire, but provides no protection against physical attacks or biotics.
• Geth Snipers, Hoppers and Primes can jam your radar, making it impossible to detect the location of enemy units. Killing them removes this effect.
• Geth Snipers and Hoppers need to paint their target for a few seconds before firing. Use this time to seek cover against them.
• Neural Shock is useless against Geth, but the other tech attacks are very effective.
• Geth Repair Drones will fully restore the health of other Geth unless they are killed quickly.
• Flying creatures like Geth Drones are immune to physics effects like Lift, Singularity and Throw due to the mass effect field they use to hover.
• Geth Hoppers use beam powers that can damage your shields, disable your powers, or overheat your gun.

• Krogan are extremely tough, have incredible regenerative abilities, and have some natural resistance to biotics. Luckily the heavy armor they wear leaves them very vulnerable to tech attacks like Neural Shock and Sabotage.
• Krogan often go into a rage when wounded or surrounded, charging directly towards their enemy.
• Krogan have very strong melee attacks that can quickly kill any foe who gets too near.

• Rachni are resistant to biotic attacks, and immune to several tech attacks, but their lack of shielding makes them vulnerable to gunfire.
• Most Rachni attacks do toxic damage, which greatly reduces the effectiveness of First Aid.
• Rachni attacks move slowly enough to pass through shields, but armor plating is still effective against them.

• Thorian Creepers and Reaper Husks are very resistant to damage, but must get close to you before they can attack. Keep them at bay with powers like Lift, Singularity and Neural Shock.
• Thorian Creepers are immune to most tech attacks, since they do not use biotics, tech, shields or technological weapons.

• Asari are highly resistant to biotic attacks, and tend to wear light armor that is resistant to tech attacks as well. Light armor offers little protection against gunfire however.
• Damping mines can prevent Asari and other biotics from unleashing their devastating abilities.
• The Barrier power used by Asari Commandos compensates for their weakness against gunfire by increasing their shields. Try to disable them quickly, before they get a chance to use their Barrier power.

1. Make sure to check the lockers for your party members between missions to make sure everyone has the best gear.
2. Uncharted worlds can have points of interest other than the ones marked on their map; drive around and explore.
3. Pause combat by using the bumpers - this allows look around and assess the situation.   
4. Watch for explosive canisters, they can make combat much easier.
5. The Thresher Maw needs flat land to travel so beware when driving over flat open areas.
6. Sometimes rushing into a fight can provide you with better cover than that on the outskirts.
7. Have a henchman use first aid to allow you to focus on other skills
8. Some kinds of armor have hidden abilities (such as the devlon armor providing immunity to environmental effects).
9. Make sure to choose party members that supplement your Shepard's abilities. The right team combinations have no weaknesses.
10. Work on one of at least charm or intimidate. There are opportunities to exercise them right from the beginning of the game. It can really alter the completion of quests.
11. When entering a new system, take a moment to look at all the planets and asteroid belts without moving the map for a few moments. Sometimes, the Normandy's sensors will pick something up, and a brief flash will appear on the map. Scan that flash, and you won't regret a thing." -this leads to Minerals, collection quests, and an entire UNC, in one case.
12. Crowd control is key, in some cases. Use an adept to full advantage by merely allowing them to take some of your enemies off your hands for a while.
13. One of the biggest traps to fall into is to spread yourself too thin… Focus on single skillsets that complement each other, instead of multiple ones that conflict.
14. When possible, engage enemies on foot. There is more experience to be gained while on foot than there is sitting inside the Mako and picking off enemies from a distance. More fun and strategy, too.
15. Not every world in the universe was meant to keep humans alive. If you're going to a world where the hazards are just too much for you to handle, keep an eye out for Devlon armor. It only takes one team member to be equipped to save yourself from dying of exposure on some remote planet.
16. Krogans are tenacious and frightening, but they are also NOT team-oriented. If you come across a few Krogans, try and lure one away from the pack and take them one mano-a-mano.  
17. Your followers had lives before they met you. Talk to them, ask them about those lives, and they might just surprise you with info about their home life, or in some cases, they will allow you to help with some 'unfinished business.' At the very least, you will learn something new about your space-faring friends.  
18. If you see a terminal that you can decrypt, then by all means, do it! At the very least, you will learn something new about the universe, but sometimes there will be some tidbit of information there that will let you explore another region of space. 
19. Not every crazy person you meet in the world is actually crazy. Sometimes, if you can get them to talk to you, you can hear their story. And sometimes, that story will make so much sense that you might think you're a little crazy, too. Try to get every person you can to talk to you as much as possible. If you don't then you might only see what 'they' want you to see….
20. Adepts and Biotics start slow. There is no denying this. It may seem frustrating, but if you work at it, it is beneficial to play a character who can constantly juggle any enemy. No one, not even a high-class soldier, can touch a master adept.
21. You have 10 save slots. Use them!
22. The galaxy will ALWAYS need saving. How long it takes you to do that is completely up to you, but keep in mind that if you save the big picture, then you lose many of the small ones. Don't be in such a rush to confront the big bad if you have the opportunity to help (or make some cash…) along the way.
23. Omni-gel is your friend. Keep at least 30-40 of the stuff around. You never know when you'll *** up on that decryption for some fantastic armor, and you'll be glad to have it.
24. Second playthroughs aren't just for the extra story you will most definitely have missed the first time around. If you have certain achievements, then you can try out some custom classes. An adept with a sniper rifle? Perhaps a soldier with AI hacking? A sentinel with a shotgun? Experiment. See what feels best for you.
25. Each new class is completely different from the others. They require that you re-vamp your playstyle, because if you don't, you will end up critically failing more missions than you critically succeed.
26. Stores tie their supplies to your level, so if you find that you aren't getting the equipment you want, leave, find some new worlds to explore, or quests to complete, and then come back to see the new shipment. 
27. The Citadel is the hub of the galaxy, so there's always something new to see/find. Come back often to see what you may have missed. It might be a large place, but exploring it again is well worth the time.
28. Choosing your background in the beginning of the game may seem trivial, but it really isn't. Characters interact with you differently, and even some missions are tied to your past.
29. Spend points in your Charm or Intimidate persuade Talents before you get to Virmire. You'll need them to sway Wrex.
30. The easiest, least frustrating way to "solve" the AI signal puzzle on the Citadel is to shoot the power source.
31. Target Assist under Gameplay in the Options menu can be adjusted to change the sensitivity of your weapons' auto-lock feature.
32. You can adjust tactics for your squad by changing Squad Power Usage under Gameplay in the Options menu.
33. Balance your party with a mix of combat, tech and biotic skills.
34. You can climb up on some ledges by approaching them and pressing "A"
35. Specialized ammo upgrades are available that do bonus damage to organics and synthetics. Match your equipment to your opposition.
36. Equipment upgrades can be swapped no matter where you are. If you acquire a useful upgrade, add it to your equipment immediately - don't wait to return to the Normandy.
37. There are equipment lockers for every member of your crew in the cargo bay of the Normandy. These allow you to change each party member's current equipped weapons, armor, and upgrades.
38. You can set your own destination waypoint on your Map by pressing A. This waypoint will show up on your radar. Note: you can only have one active waypoint on any given map.  
39. To unlock new items in stores, purchase Manufacturer Contracts.
40. Hammerhead ammunition does little damage, but can knock targets down. Use it to keep enemies on the floor and helpless.