I’ve compiled a big list of 3A resources and I do my best to keep it circulated on all the boards as best I can, so here it is. 
A little bit of information regarding string shortening:
The shorter your string is, the faster you’ll be able to go. However, shorter string makes it harder to do complex string formations and after a certain length you don’t get enough spin in your throws. I personally recommend taking off 4-5 inches for a start and then messing around to find what you like the best. I personally just shorten to the bottom of my belt buckle, but there’s a lot of variation. For example, I did the majority of my learning (and 4 or 5 videos) on completely unshortened string and Yuki Tanami (2005 Japan Nats Champion) uses really really short string.
I wrote a little thing a while back that I was gonna put on a website I never got around to making. It’s about AAA fundamentals and some other stuff.
"The most important thing you’ll need to start 2-handed yo-yoing is… two yo-yos. Whoo! If you had already figured that out, go bake yourself some cookies or something. Anyways, the two yo-yos don’t need to be the same kind of yo-yo; it helps if they are, 'cause then they’re balanced for rolls and weight and they’ll spin for about the same amount of time, etc. etc., but don’t let different yos stop you. And if you really want a pair of yo-yos that are the same, pick up a pair of Freehand2s, they’re cheap and work well.
So, now you’ve got a yo-yo tied to each finger. Good! Remember how when you were just starting out yo-yoing the string would cut into your middle finger and it would burn and ache until you got a callous two months later? Well, unless you’re a 2A player, you’ll be getting that all over again with your other hand’s finger. Just think of it as the badge of a two-handed yo-yo player… but I digress. Your weaker hand is weaker than your stronger hand (go figure) and doesn’t have the muscle memory that your strong hand has, but since you should know all the basic principles of yoing you’ll be OK. A lot of people (read: everybody) have trouble when they start out because their weaker hand’s throw is so bad. Don’t worry about that, it’ll smooth out over time and with practice, but something that might help a lot is relearning tricks on your weak hand. Don’t try and relearn every move in your repertoire, but try and get at least the mounts and frontstyle tricks down: it’ll help you pick things up a lot faster. Seriously, just try doing mach-5 with your weak hand. A little weird, eh? Don’t worry, you’ll get used to this sort of thing.
You’ve gotten that down? Good. Now, onto the actual 3A tricks!
Start by throwing both yo-yos straight forward. Then get them both back to their respective hands. Double binds can be really ugly and time consuming when you’re starting out, so playing at at least tug response might be a good idea. You’ll want to figure out what kind of throw works best for you - I throw my left hand yo first and then my right hand yo, because that way I can re-throw the left hand (weaker hand) yo if it turns out that my first throw was crappy… rethrowing wastes a bit of time, but it’s better than having your yo stop spinning midtrick. Some people throw both yo-yos at the same time, but those throws are a bit more difficult when you’re just beginning, so whatever.
Yes, this is all really elementary stuff, and sorry if it’s boring, but trust me: it’ll help.
Sidestyle throws are the same thing, although it should be noted that sidestyle throws spin away from each other so keep that in mind for suicides and other technical tricks you might come up with, and also remember that you’ll be throwing straight down more often than double breakaways. Unless you’re doing double trapeze or something like that. but you know what I mean.
It’s safe to assume that you’re bored to tears with this section, so let’s move on, shall we? Probably the easiest house (that’s a AAA buzzword meaning “class of tricks”) to start with is Assisted House because pretty much all it is is 1A tricks with a yo in place of one of your free hand. If you haven’t checked out all the tricks on the Worlds Compulsory Tricklist, it’s about time that you do. House Kink, House Velvet, and Magnum Rolls all offer good “easy” tricks to learn and have harder variations that you can move into. Frontstyle stuff, as a general rule, has easier beginning moves. Shotgun House also reportedly has some pretty good beginner moves, but I can’t do any of them, so I’ll just tell you to go learn them from my esteemed colleague Tim Simco.
…that’s as far as I got with it. Hope all this helps.
Cheers!