Murphy's Laws of Combat

Some classics:

7. Try to look unimportant; the enemy may be low on ammo and not want to waste a bullet on you.

23. Teamwork is essential; it gives the enemy other people to shoot at.

25. Never draw fire; it irritates everyone around you.

51. Sniper's motto: reach out and touch someone.

55. When in doubt, empty your magazine.

101. There is always a way, and it usually doesn't work.