There are loads of little tweaks and tricks you can do to improve your aim but only serious gamers do this who play in Leagues and get paid to play in competitions on in clan matches.
But with the aiming in Battlefield 2 as annoying as it is anyway, when you shoot a few bullets your accuracy will completely go crap. And to reset your aim, you must go from Standing, Crouching then to Prone, then go back to what ever position you want. And by doing this your next few bullets will be perfect where ever you aim. (But as I said, only serious gamers do this in competitions)
When ever looking down the sight of any gun in BF2, never burst (unless they're fairly close, but then again you should aim if they're that close) your gun, always single shot it or if you have an option to burst with your gun use that (press "3" in game to change your rate of fire).
Another little thing in BF2 is if you shoot your gun at someone with out looking down the sights that can be more accurate that when you do look down the sights. It's best to try it with a Machine Gun like an M16 or a Ak-74. But if you just prone whilst using these guns and just single shot an enemy by using your cross hair it is more accurate and you will see your Cross hair blip in the middle as an indication you've hit your enemy.
I would go into detail about the classes but you can find better guides through Google.
With Anti Tank kit, I saw you kind of doing what your meant to do whilst using Rocket Launcher.
If you see a tank, and your behind a barricade you can prone behind, scope in on your Rocket Launcher, aim at the tank, shoot, then go prone and using your head remember where the tank was and aim still whilst your behind your barricade, it will go exactly where you want it to as if you were standing up looking at it. By doing this it stops the tank using it's secondary fire machine gun.
The Medic class is the most used class, since when playing in a clan match only a medic kit is needed and that's what everyone will use, since you can heal yourself and revive team members.
When running around as a Medic and you see someone, throw a medic pack out in front of you then get your gun out and shoot back, and when your medic pack gets used, throw another one out. They will never run out, your have 3/5 on you anyway, but once you use those up you have a recharge bar until you have another one, but don't wait for it to recharge if you run out of medic packs, just run to a different location and next time you check you'll have stocked up again on Medic Packs.
Have you got the latest patch? 4.1.
If not here's a few links,
It's a 500 mb patch. But you don't need any other patches.
FileShack ( Requires Sign Up )
http://www.fileshack.com/file.x/9046/Battlefield+2+v1.41+Patch
FileFront ( No Sign up )
http://files.filefront.com/Battlefield+2+v141+Patch/;6194285;/fileinfo.html