One other tip I found as a recent AR newbie.
I was very used to my M1-A front sights, which are .062 inches wide, and great when shooting long distances, but I found the standard front sight post that comes with AR-15's is very fat, and when shooting beyond 50 yards, you can really improve your accuracy by replacing the standard A-2 front sight with a Bushmaster Competition (or any other company) front sight.
They screw right in if you get a pen and push down a little button on the front sight that holds the front sight in place. They're on pg 16 of the 2002 catalog and only cost about $12 bucks plus shipping. I put the .052 inch wide sight on mine, and have a clear view of small targets at 100 yards. The standard front sight post looks like a telephone pole in the way of your target when aiming 100 yards plus.
You'll see this fat sight situation if you just pick out something at 100 yards plus and take aim at it. A thin sight helps you see much more target.
Another cheap alternative I've read here that some people use, is to just file your A2 front sight thinner, as replacements ones are only $5-$7 bucks.
BTW- just shipped my AR to Bushmaster for repairs recently, alot of them need the front sight to be re-indexed, as when you zero it in, the rear sight has to be very far to the left or right. Bushmaster will fix this for you, and pay shipping.
Have fun, and don't worry about new stuff for the gun at first, just get comfortable with it, then think about buying a new front sight and some 30 round GI mags for it. Make sure they're GI mags, not the "USA" brand magazines, as those don't work.