two pets at a time,i have one pet that i maxed out for certain abilities,you know,the speed and strength things.you don't have to max it out,just use it in battles,and every time you log in,go to the pet pavillion and use that pet in the games at least two times er game,every time you do that,your pet will grow a lot stronger,every week,switch pets.
If you have so many pets, you should focus on one at a time. A great way to rank your pets up fast is to buy one of those Mega Snack Packs for 2,500 crowns. High ranked pet snacks will help your pet rank up fast.