http://ar15.com/content/
Start there, have a look at the various files on the page, some may be of help to you.
I'll recommend practicing your magazine changes quite dilligently...I had my team practice their mag changes up at the nationals, and we had guys who started with a 7 second mag change (from time of last round fired to next round fired.) Obviously, this is a bit slow for competitions...7 seconds is almost 1/4 of the time that's allotted for a rapid fire match....UNSAT. I had the guys bomb up single round mags and two round mags and practice their mag changes for about 20 minutes in the various positions (prone, sit, kneel, stand) until they were somewhat speedier. The 7 second guy ended up at around 3.5 seconds by the end of the practice.
Now, a 20 minute session is not enough to build all the needed muscle memory, but it does give you a good start on where you need to position your mags, and what motions you have to make in order to get at the mags in the different positions.
So, anyhow, there's some stuff to start with, more folks will probably chime in with various responses, but my suggestion is to grab a case of ammo, and go practice.
NS