Okay, this will not be a very long tutorial, but I want to share with you my aiming methods.
Four aiming methods:
1. Crouch & Shoot ( full accuracy )
2. Hybrid aiming ( combination of speed and accuracy )
3. Increase opposition ( not really an aim method, but overrides these aim methods)
4. Rush & Spray ( fast )
5. Head shot Practice
The main key is burst fire for accuracy.
1. Crouch & Shoot
Self-explanatory, immediately stop and crouch when faced with an enemy to easily shoot them down with full accuracy.
2. Hybrid Aiming
This is my favorite method. First you must test the guns by using them on a wall. Make sure you shoot three-round burst at the wall, and you at a good distance from the wall.
Test with these methods:
1. Run & Shoot
2. Walk & Shoot
3. Stand & Shoot
4. Crouch & Shoot
See what one is the highest speed with enough accuracy.
Examples:
Code:
MP5 - Run & Shoot
M16 - Stand & Shoot -- Crouch for long distance
K-2 - Walk & Shoot -- Stand or Crouch for longer distance
( *Tested and works best for me )
3. Increase opposition
I suppose this is the more "tactical" method. I use this when Hybrid Aiming has been failing me. Basically, when you are faced with an enemy, pay attention to the direction they are running. You run the opposite direction.
Examples:
Code:
Faced with an enemy strafing left - I strafe right and spray
Faced with an enemy standing - I stand/crouch and burst fire
Faced with an enemy strafing right - I strafe left and spray
Faced with an enemy running towards me - I only use W or S ( up or down ) and decide between spraying or burst fire
Faced with an enemy running backwards - I only use W or S and decide between spraying or burst fire
May seem odd, but it works for me
4. Rush & Spray
This is the last method I go to. For some reason, this works wonders sometimes though. So DO NOT use Jump, Backward ( S ), Walk, or Crouch and run towards the enemy full blast spraying. So by default: UNBIND S, SHIFT, CTRL, and SPACE. It may seem to be an odd and un-pro method, but it works against newbies to the game. Do not attempt against pros, or prepare for your game play to be bashed.
5. Head Shot Practice
This is one of my favorite methods as well. This is where you only head shot the enemy. If you struggle with this, find a friend that will do pistol matches with you and agree to do only head shots. Set up a private match for you and your friend(s) and practice head shots to each other. Make sure you are all playing seriously, or you will not gain any skill through this ( FYI, NOT FARMING
) This will greatly improve your aim, get you more head shots which, oh by the way, are a one shot kill for most weapons, and you will probably end up killing more people if you are fast enough. You can also just do a normal pistol match and let your friend aim wherever on you and you just head shot him. I find this is worse practice though.
When you are tired of pistol, you can move to the automatic weapons, and practice with those to see if you have improved ( I have
)
6. AIMBOT
Oops how did this get here?
Well those are my methods. I hope you can do better in Cross Fire now and show off to your peers 
You will have to test each method and see what works best for you. Once you find what is working best for you, you may very well achieve higher K/Ds!