The simple things are always hard. When you have secured an area, don't forget to tell the enemy. Incoming fire has the right of way. No combat-ready unit has ever passed inspection. No inspection-ready unit has ever passed combat.
Teamwork is essential.
It gives the enemy other people to shoot at. If the enemy is in range, so are you. Friendly fire isn't. Tracers work both ways. The only thing more accurate than incoming enemy fire is incoming friendly fire.