Well, I use the standard rules.
Those are : No Uber Pokemon (but you can use the other legendaries). Here a Uber List :
http://livinglifecasually.com/forum/showthread.php?t=1753
No same Pokemon - which means that you can't have 2 Tyranitar or 1 Tyranitar and a Larvitar.
No One-Hit K.O. Attacks
No Hypnosis Attack.
I've forgot the 5th clause...