So I gave in and bought SC2. And I love it. It's the first non-Nintendo game that I enjoy playing.

I'm starting from no RTS experience at all, and a few days of practice later I can consistently beat the AI on Hard, Terran v Terran.

How best should I proceed if I want to learn the game well enough to play ranked multiplayer and enjoy it/win occasionally? Fight harder AIs? Try all of the races? The single-player campaign? Challenges?

And how will I know if I'm ready to do it?

One specific problem I'm having is that while I've sent a group of units out to fight I have to watch and micromanaage them, leaving resources at my base piling up and my production structures unused. Is there some magic way to multitask, or is it again practice?

How best should I proceed if I want to learn the game well enough to play ranked multiplayer and enjoy it/win occasionally? Fight harder AIs? Try all of the races? The single-player campaign? Challenges?

*sol: So challenges are somewhat useful for newer players. They help by showing which units are better than others. The usefulness of units etc. As well as micromanagement. Single-player campaign not sure how that will help you that much. Harder AIs will help but to make sure you get better try to beat them as fast as possible. Some friends I know take the long route of beating them. But in terms of multiplayer you just have to get good at micromanagement and beating a higher level AI at a faster pace helps.

One specific problem I'm having is that while I've sent a group of units out to fight I have to watch and micromanaage them, leaving resources at my base piling up and my production structures unused. Is there some magic way to multitask, or is it again practice?

*sol: So you could hotkey your buildings to a number like a group of units. So say your units are 1-3, just hotkey your buildings to 4-5 etc. Thus while your in fighting you can just press they hotkey and spam unit production

How is the playing style of multiplayer different from AI play?

Indeed, it is not about multiplayer

it is about good player vs bad or beginner player

Usually, new player tend to purchase mass tower/bunker and to wait late game to attack their opponent. they also have tendency to accumulate a monstruous amount of money.

while good player will be agressive as soon as possible with otpimized build order, map control as soon as possible, rush or harassement to keep the adversiare on the defensive and they will not accumulate ressource.

you have to be efficient as soon as possible because if u left the enemy accumulate a bigger army then you, then, it is dead for you. Plenty of game do not even take 10 minute to finish ...

about the IA :

I would say it is mostly less agressive : he will not come directly at you as soon as he has unit.

I find watching some YouTube videos helps me a bit. Watching the top players gives you some decent strategies to try out add your own little thing to.

Learn every map. Learn what units are best for countering other units.

Learn the best way to create choke points, and the best way to set up your base.

Learn strategies like this -

http://www.youtube.com/watch?v=i0LA6DNvF4M&feature=related

huskystarcraft and HDstarcraft channel are awesome !

I would suggest jumping out there, the practice league games should ease you in and playing is one of the best ways to learn (at least for me) just don't get discouraged when you lose because online especially when you get into the ranked leagues you most likely will lose 50% of your matches if the matchmaking is working the way it should. 

EDIT: One major difference between online and AI is humans are far less predictable, they will try stuff you probably never would have thought of. It is also a good idea to at least play around with the different races so you get an idea of how they work even if you don't play them online.

I sure haven't played SC2 but a good general rule seems to be learning the effective strategies/tactics. Someone mentioned watching videos and might give a good idea. Personally I consider experience the best way to learn, ie. you should just play and try to improve your strategies and tactics. But that can be pretty annoying since unless you get the hang of it very fast you'll get your ass kicked. Thus you should also know gameplay mechanics, units, building and all such rather well. Which I suppose you already do.

Anyway, knowing your enemy is also good. Try to think like your enemy, try to guess what they are going to do. And all the time you should be unpredictable yourself, though that might be a bit hard at first so you should concentrate on other things.

Edit: yay, my post didn't post. It was way too much to retype....