Please help me get gud at Pokeman.

I'm playing x, have finished the game, and I struggle when playing random battles online. I usually use Snorlax with rest, stockpile, bellydrum and crunch. Mewtwo with default attacks, and Charizard with fly, flamethrower, wing attack and flame charge (?). I also have a gengar with hypnosis and dream eater.

What are some OP pokemon or builds I could use?