I just do a lot of battles. I don't really create teams with the specific mindset of joining tournaments, but I'll join a few if I'm bored and have nothing else going on. Battling is the only way to prepare in my opinion. It helps smooth over weaknesses and it helps you find out different strategies with different threats. If it weren't for battling a crazy amount, I would have never figured out to throw Jumpluff out against fire teams first to counter Ninetales.