Don't know if someone's said this already, but Murphy's Laws of Combat could have some good suggestions, specifically:
1. Friendly fire - isn't.
2. The enemy diversion you're ignoring is their main attack.
3. The easy way is always mined.
4. Never draw fire; it irritates everyone around you. (important)
5. Anything you do can get you killed, including nothing.
6. Make it too tough for the enemy to get in, and you won't be able to get out.
7. Tracers work both ways.
8. When in doubt, empty your magazine.
9. Air strikes always overshoot the target, artillery always falls short.
10. The bursting radius of a hand grenade is always one foot greater than your jumping range.
11. Every command which can be misunderstood, will be.
12. NEVER get into a fight without more ammunition that the other guy.
13. Sometimes, being good and lucky still is not enough.
14. Hope for the best, but prepare for the worst.
15. Failure of plan A will directly affect your ability to carry out plan B.
This is only 15 of the ones I thought were important, this is a full list.
Murphy Laws Site - War Laws