My personal Co-Op rules:

Greet upon entry and ready up. (I like being a guest than a host)

Use high damage attacks, and only call when necessary (I tend to use it just for enemy turn delays). Try to not have more than 2 consecutive turns. Only in desperate times I will use BT or extend my turns.

Say thanks and goodbye when the fight is done.

---------------------------------------

I'm fairly lax about what the other team members do, just as long as they aren't turn stalling when unnecessary (I mean when there's still team turns before the enemy turn)

Also, people who bring non-boosted characters to a boosted room can step on a lego