While Practice can't hurt, its probably most beneficial to aquire as many battle pets as you can. We still have to see what new pets and abilities will be nerfed for 5.3.
"Sucking" in Pet PVP is far more easier to fix, than "Sucking" in Player PVP
You have time to contemplate your move, only have 3 or a possible 6 moves to use per pet, so it is not really about quick decision making and good keyboard mouse dexterity. It is alot more about team composition, and having enough pets to choose from to make your winning team.
As strange as this sounds, one of the better preperations for expanded 5.3 pet PVP has nothing directly to do with pets at all.
This way, if you dont have time, or connections needed to get new raid pets, you can always buy them.