It's amazing how much you can learn just buy watching and immitating the guys.

For a speed bag, start out slowly. Us your good hand to start. Hit it... let it do what it wants, then hit it again. Just keep doing this... with one hand until you get a feel for where and what your hand should do in between hits. Then hit it a bit harder...just hard enough so it can make  3 hits with the platform. Hit it a second time when you know you can. If you hit it every 5 bounces, fine. Do that until you get confortable with it. Then try hitting it once or twice AFTER it takes 3 bouces...ie, 2-3 strikes in a row. Hit, bang, bang, bang, hit, bang, bang, bang, hit... etc. At this point you'll f up, if not after the first time you hit it. Once you feel comfortable, incorporate your second hand. Then do 2 hits left, 2 right, with maybe 5 bounces in between. You just want to develop a feel for knowing when to put your hand in the way of the bag on it's way towards you.  You want to learn how to hit it every 3 bounces as slowly as possible. Don't think of it as a speeg bag at first. Think of it as a control bag. Pretty soon, the bag will appear almost as a blur and the only place your eyes will focus is on the down-swing after the 3rd bounce, at which time your hand will be there to crack it.

Also, a lot of guys hit it with the side of their hands, like a karate chop with a fist. Me, I do 2 left, 2 right, shifting my weight between feet and bringing my non-striking hand to just under my chin. Other ways are l,r,l,r,l,r etc. and only hitting it on one side of your head. ie, off to the side.