To do a boost-start you just hold X and A from where it shows the racers to when it says "1" in the count-down.Then let go of X (but continue holding A)and your bike will boost forwards.
Get new bikes and levels
To get new levels and bikes you have to beat meets. I haven't gotten all the bikes or levels yet but I'm working on it.
Grand prix mode
Go to time attack and beat the best record. This will unlock GPM FOR single & mult.
All tracks
Get gold medal on every thing in license.
Various Tricks
Wheelie: Hold the Left Analog-stick Back.
Standing Wheelie: Press Trick + Left Analog-stick Back.
Surfing Wheelie: Press Trick + Kick/Punch + Left Analog-stick Back.
Cross Surfing Wheelie: Press Trick + Left Analog-stick Back + Front Brake + Kick/Punch.
Endo: Press Left Analog-stick Forward + Front Brake.
Surfing Powerdown: Press Trick + Left Analog-stick Forward + Power Down.
Handstand Powerdown: Press Trick + Skid + Left Analog-stick Forward + Power Down.
Surfing: Press Trick + Left Analog-stick Forward, then Left Analog-stick Back.
Handstand: Press Trick + Left Analog-stick Forward, then Kick/Punch
Pavement Ride: Trick + Left Analog-stick Forward, then Skid.
Donut: Hold Brake + Gas and turn in one direction with the Left Analog-stick.