Well, so long as we're sharing:
I personally restrict myself from using traits or tactics I consider unbalanced or cheesy:
No Glass Cannon
No Lone Wolf
No Leech
No Zombie
Invisible can only be used to pass by enemies; you can't open doors or take things
No cheesing fights. That means that if I didn't know I was walking into a boss encounter, I can't make pre-battle preparations like setting traps or positioning people ahead of time. I am allowed to scout ahead if something is obviously up, but I'm only allowed to set up a trap once I've actually physically seen the enemy.
Also, no positioning people during dialogue. It's a cool mechanic; I like the idea that my guys can sneak behind the dumb villain while they are talking but at the same time it's kind of lame that I can just pause the conversation indefinitely while I have someone else coat the area in oil barrels in full view of the enemy and all their henchmen.
I also use the source difficulty mod so that enemies have enough action points to actually fight back. It makes healing and CC a lot more important as I can't simply rush in and one shot everyone with my warrior.
