Alright so its not really that huge but I figured it could help a few people! At least it helped me!
So when you're up against a hunter, take down his pet - if he doesnt have a pet with heart of the phoenix well I guess that's just perfect - but if he does:
The pet will automatically heal up to 100% hp upon resurrecting - however there is a small period of time where the pet only has ~5% hp before this instant heal happens. Now if you hit the pet in that short time, it will die instantly and you wont have to worry about taking another pet down from 100% while its getting healed etc! I guess this mainly works for classes with high damage instant attacks, like arcane mages, rogues, retpaladins, death knights, warriors and hunters - but yea it won me a few games!
So basicly when the pet dies you target it and spam your instant ability on it to instantly kill it of a 2nd time when it ressurects!