Low ping and smooth fps are both factors that make it easier to aim. It's a lot easier to get headshots with 70 ping than 150.
Remember that moving makes the spread worse, while crouching makes it better (this is not vanilla q3). Moving while crouching is about as good as standing still upright. Don't fire while in the air, wait until you've landed, except maybe for shotguns. Spectate players that kick your ass to see what they do (no, they're probably not cheating).
Boiler plates are good (but don't protect you against knives or Sharps), ammo belt is a cheap way to get lots of ammo. Move around the map to get more frags, listen to money pickups etc. to know where people are. Try to circle in on people when you're low on ammo, pull out your knife when you're close enough and they can't get away. Bind crouch, knife and reload to keys you can use without letting go of movement keys. Blah blah blah etc.