For those that played Pokemon and have experience playing trading card or turn-based games, Pet Battles will probably be easy to pick up and dominate in. But if you're like me and you really don't have much background in these areas, it might take some trial and error before you can "be the very best" lol.
That isn't to say I'm not enjoying myself. I still am since this mini-game is pretty easy to pick up. Plus I'm not a complete fail against pet teams haha. (I have yet to try against another player, though. :P) But I know that with more knowledge and practice, I can get even better and eventually build my ideal team(s).
Here are some good resources for understanding Pet Battles. Most of it covers the basics and there's (a lot of) information that's repeated, but there are gems of details within these write ups that might be useful, especially for those who are just getting started.
Twitter! I'd love to add more resources to my list. You can never have too much knowledge.
(Unless you see what can't be unseen and your mind goes crazy from absorbing what can't be understood. *cough* Cthulhu fhtagn *cough* XD)