1) Give Frederick the Avatar's Bronze Sword. This not only helps him survive missions two, three (ohhhhh...mission three.....) and five when all those axe users swarm him (yes, I said "survive"), but it also stops him from outright killing most foes, letting your other characters reap some experience.

2) Use the pairing system often, especially for the avatar (even if it's just with Lissa). The bonus XP will literally be a lifesaver in the early going, as your avatar can hit level 10 fairly easily this way. Other units will need that extra oomph to not get double-shot.

3) Later on, start stocking up on Rescue wands. I found it ridiculously helpful to have a strong unit bum rush the next wave's biggest threat, and then pull that unit back to safety before it got swarmed.

4) Recognize that only Frederick, Chrom, and the Avatar are going to be able to survive most enemies' attacks, and plan accordingly.

5) Don't hesitate to Frederick abuse. He WILL do the bulk of the fighting for the first few missions, especially on levels three and five.

Not much i can add.  Have you beaten Lunatic?  I'm still too low stats for final mission atm.

I stuck to mostly Chrom/Frederick with Avatar/Lissa in the back.  I reset if Fredrick or Chrom get crap stat ups at the start (Str, Spd, Def are must early on).

Once you get past Chapter 4, grind a bit from the DLC to play catch up with units that weren't Avatar/Chrom/Lissa. I did this to get Sully and Vaike up to speed. 5-10 Levels all you need.

And Resuce staff is like the only way to save Ricken Or Marribelle in Chapter 5, unless you grinded out the wazoo from DLC. 

Thanks for the tips mates! I'll be sure to try this stuff out! Seems that Rescue Staff is for more than just easy experience hehe.

They are the cheap man's Psychic.

But man Psychic is addiction for late game healers, they get like NO exp ever.  And minus Libra, putting them into combat is a no no (Stares with eyes of disappointment at Lissa's 24 def).

Yeah. That last mission is a total pain in the ass, though. Eventually I just paired up all the A-and-S-ranked units and bum-rushed the boss (fliers and other high-mobility units do the moving, then fliers in particular get switched with their partner: the bonus stats provided by Cynthia and Olivia were great, but they would have been easy prey for all the bows and wind-magic users).

It somehow worked, as this let me avoid ever fighting the many, many units on the bottom of the map, but I won't pretend luck didn't play a huge role in getting everyone out alive: at one point, Kjelle negated the enemies' attack three times in a row, for example. The problem is that slow and steady just gets you overwhelmed: it wouldn't be so bad if I knew ahead of time where reinforcements would warp in, but I repeatedly spent twenty minutes methodically working my way down and then up the map, only to lose someone to an Assassin. Grrrrrrr....

It's doable though, even without grinding. Admittedly, I'd planned pretty much everything ahead of time for that no-grind run, and got lucky on a couple (several) places, but it's doable.

I will say I disagree about the Rescue staffs, though. Psychic is great for healing, but the way I used the Rescue staff let me preemptively take out a big threat, while also ensuring that my unit wasn't consequently surrounded by foes. So, for example, my Dark Flier could charge a mounted or flying unit using a Beastkiller, then get pulled back to my lines and live to tell the tale.  I honestly don't think I could have beaten the game without using several of them. Which is surprising, because I never used them at all on Hard or in previous games.

Well as a slow and steady kinda guy I just need better stat'd units to make it work.

My problem was also getting overwhelmed, even with the final boss almost dead. 

Dealing with Ignis procs every attack BS is enough to handle. ;p

Tho the boss of The Strongest's Name DLC makes the final boss of the main story a puppy in comparsion.

Heh, on my previous files (especially the Chrom only one), I just zerg rushed "the boss" (would it be a spoiler to say it's name? I figure it'd be kinda obvious who the final boss is), having to reset until I got lucky. Last mission so I figured it pointless to try and kill other enemies. :L

With the European launch so close I just figured better safe than sorry.

I got a post moderated for posting a picture of Chrom's reaction with running into all the children characters over and over (and I think it was towards Cynthia).

Can you use rescue on an npc?

Or healing staves in general on them?  Never tried strangely.

But just thinking of Severa's level.  I did manage to beat it, but damn was she pissing me off.  So many times did I have to replay cause she would run to a spot where she gets one shot or something.  Sometimes due to my neglagence and forgetting about her, but a few times there was nothign i could do.  Then of course didn't anticipate teh spawning when she finally talked to the village guy.

But woudl be awesome if I coudl have had a healer just sit back and rescue her away while I clear the map, then follow her up to the villager.  If rescue works on her, I will definately do this on lunatic +

Yes you can use rescue/healing staves on NPCs.

Minus the DLC called the 5 Annas.