Tongue in cheek: Make Peach top tier.
In seriousness, I consider myself a student of game design. Obviously, stuff like random tripping has to go, but the issues with Brawl are actually very subtle.
They stem from one fact: Brawl rewards defensive play too much.
This reward on defensive play drives Brawl gameplay to be a slower hit-position-react gameplay. It's actually still a very deep game, but it's so much less watchable because there is so little reason to approach. It's like how chess is a very deep game, but there is no audience for chess games because it is super boring for non chess players to watch.
Football by comparison can be watched by people who don't play the game or even fully understand the strategy.
For example of defensive issues:
* Shields are extremely powerful in Brawl. You still have most of your options available out of shield, and the things that threaten you when you are in your shield are fairly minor. Grabs generally give the opponent a positioning advantage and minor damage, excepting Dedede and Ice Climbers.
Shields in Melee, meanwhile, are much weaker: shield stun reduces your shielding options, and hitstun makes grabs a much greater threat. Brawl doesn't need to nerf shields totally, but either making grabs better (via hitstun combos) or shields worse (via shieldstun) would dramatically increase the perceived value in aggressive play.
* Ledge play is simply broken. The time gap between how fast a character can regrab the ledge and when their invincibility ends is minuscule. Characters with sufficient maneuverability and certain hitbox types (Metaknight, G&W, Pit, ROB) simply cannot be given valid reason to get off the ledge.
You get thrown off the ledge when you are losing. Ledge play needs to be adjusted so as to become a disadvantaged position. Simplest way to do it is to say "no invincibility after three consecutive ledge grabs". Other alternatives include making it harder to grab the ledge (like previous games) or nerfing recoveries to reduce ledge play options. These are probably better. The key is, ledges should disadvantage the player holding them. He is barely holding on and should feel pressured to get off the ledge.
* Speed needs to be improved, either through mechanics that encourage it (hitstun!) or faster gravity that forces players back in to each other.
These tweaks should make Smash a much better competitive game.
Also, it is critical that there is a WIRED USB CONTROLLER OPTION. If not Nintendo developed, the game has to allow for third party USB controllers. I cannot stress this enough- large tournaments cannot be run with all Bluetooth wireless controllers. If wired options aren't available...big tournaments like Evo and MLG cannot host Smash Bros, period.
Also, better online would be nice, and give the game a patching function!