Your Gun
First off, have a gun that YOU are good with (anything but sniper this is a spraying guide =]) DON'T BUY A GUN THAT EVERYONE SAYS IS GOOD BUT YOU ARE NOT GOOD WITH IT
People who buy guns that are good but cant use them are complete noobs and have almost horrible k/d.
Rushing Is The Worst Thing You Can Do
This is the biggest mistake of sprayers, who rush but either get picked off by snipers, killed by a grenade, or kill another opponent but get themselves killed in the process.
Wait
In order to get a better picture of your surroundings, simply wait, or run behind 2 - 3 people. If these people suddenly die, then you know that there is an enemy waiting for you, and you can take him by surprise.
Reload
PLEASE make sure you reload after each kill. I cant tell you how many times I have pwned noobs who rush out, waste all their bullets on one person, and get killed by me. Also when you reload, be behind a box or something like that.
Crouching
Crouching is extremely important. You might wanna set crouch to a comfortable key, such as shift, because you'll need it a lot. Walking while pressing the crouch button repeatedly gives you the number one skill a sprayer can use: STEALTH. No one will be able to hear you.
Listening
PLEASE OH PLEASE make sure u listen to your surroundings. If you don't have speakers, it is probably why you have one of the lowest k/d in the game. If you are being sniped and you don't know it, you WILL hear the sound of the bullet go past you if they miss.(It will make a whizzing sound =]) Also, you will hear the sound of noob sprayers who try to shoot you from far away.
Comment if anything needs to be added =]