pwned
What I'd do, find out which gun you're most confortable with. What I mean by that is handling it's recoil, and aiming. In 1.6, I use to be awesome with the AK, getting headshots left and right. Now, I (to put it bluntly) am pretty bad with the AK and am even worse with the M4. That's what practice is for, eh?
I'm kind of on and off with the M4 when using the silencer. Sometimes using the Gali or Famas may suit you better than using the AK or M4. I know I'm starting to use the Gali more than the AK because it's not only cheaper, it's easy for me to aim with. I took out several guys when using the Gali and probably something I couldn't do if I was using the AK.
Also, practice aiming with bots. What I did in CS:CZ was put all the bots to Knives only and aiming for their head a ways back to practice my aiming.
Another thing I learned from CS1.6 was to watch skill videos. Believe it or not, it can help you get better. Watch how they aim and try to do that ingame. Watch how they react when getting hit or getting shot at. In 1.6, whenever I was getting shot from behind, I jumped, did a 180, and usually killed the guy behind me. I still do that in reflex, but I guess it doesn't really help in Source.
Another thing you could try would be to record yourself and see what mistakes you did and try to see how you can fix them.
I also just recently made my crosshair smaller. I found that the bigger crosshair gets in the way of your aiming and you can't really see if someone's there from a distance. Also, make it a color you can see well. Green and red work.
Don't know if any of those will help, but I figured it should do something.