If you suck like me, this method requires a thick skin and some time, but it works:
Play a bunch of ranked matches. (Be sure to have some hand-held entertainment around to keep yourself occupied while you wait for opponents to be found.) At first, you will be matched up almost exclusively with people who know 30-move juggle combos, and who will likely use hate speech. This will not be the most awesome time of your life.
After a dozen or so humiliating losses against teenagers who are almost always, for whatever reason, homophobes, you'll start to notice that your opponents aren't juggling you anymore. They're still mopping up the floor of the Batcave with your face, but you're actually getting a hit in now and then.
Eventually the rank system will realize just how useless you are, and you'll get matched up with someone like me. Then it should be no problem. I think I won with Green Lantern, but at this level of play, it really doesn't matter whose buttons you're going to be mashing, as long as the other guy does it more poorly.