Work on mario's edge game. Exploit it to its maximum. Mario can work wonders off the edge. Learn how to release the edge and to certain moves like the bair, uair, fireball. Learn how to cape stall away and towards the edge, and/or connect it within moves. Exploit the fact that pressing the jump button off the edge gives slight invincible frames, with that note, don't be afraid to pull off a nair quickly after the initial jumping animation for a nice invulnerable quick attack.
I believe monk is exceptionally well at this, watch his vids.
On the side note, learn how to RAR marios arials and the hyphen usmash...