Anyone have any tips for Super Smash Bros. Melee?

I'm going to be in a tournament next month. It's a melee tournament at Game Crazy with the final round being on Brawl. (Midnight release) but for the past few tournaments I've done... craptastic. I've been trying to master Fox, Mewtwo, and Roy in addition to the already mastered Marth. So any tips would be greatly appreciated! (First prize is a copy of Super Smash Bros Brawl)