Im gonna post what i know about this.
You can practice fancy teamwork all you want, but its not gonna do ya much good if ur not good at the game.
Each player works as a singular unit, it is this players responsibility to eliminate the enemy units.
The best way to easily eliminate more than one enemy is to exploit cover, and take them one at a time
NEVER rely on a team mate to come save you, because a majority of the time they wont.
Dont waste your grenades, use them to flush out any enemies who are using cover.
When you kill your enemies, you may then assist your team mates with their enemies.
The most important advice i can give is: STAY AWARE.
Check your radar constantly, listen for footsteps and LOOK AROUND YOU.
Often when you have a task in your head, such as ambushing an enemy, you focus only on your task.
Look past just your objective, because nine times out of ten there's gonna be an enemy in your way ready to stop you because you didn't notice them first