I found this easiest to do with Sinestro.
I mostly used 2 moves and added a meter burn when I could. The two moves were:
Down, back, Y - Drop a boulder on the enemies head
Down, forward X - Shoots an energy ball
The trick is to keep away from your opponent and keep spamming these attacks. When you build up at least one portion of meter, press RT shortly after either attack and you'll do a more powerful version of that attack.
If your opponent gets close try to use an environment object to get some distance or attempt a throw.
Using this method I went from winning 1 in 3 matches to almost every match. There will still be times when someone very good at the game will thrash you but this method should get you 10 wins very quickly.