No team killing. We are a co-op clan. Make sure of your target before you shoot. Turn on player markers if available so that you know friend from foe. Likewise do not trash our base or friendly equipment.
Follow your squad leader's orders. Many of these missions can only be solved by teamwork. Hold fire unless fired upon first or your leader calls out "weapons free", "engage at will" or a similar command.
Maintain radio discipline. While it is not totally prohibited to engage in idle conversation, you don't want to tie up the voice channel so badly that you miss important reports regarding enemy movement.
Do not attempt to pilot aircraft unless you are adequately skilled. The time and place to practice is in single player mode or in training missions.
The enemy hears noise and reacts. Maintain noise discipline. Don't spoil a good ambush. Some missions can only be won if the element of surprise is on our side.
Drive carefully and in the directed formation. The equipment is needed for a successful mission and in many cases it won't respawn and there will be no repair facilities. If you do wreck a vehicle it is your responsibility to retrieve and repair it if possible.
Game specific rules will be posted in the forum for that game.

The only addon used on our OFP server is editorupdae102. This is commnly available if you don't have it already.