Get Squashed by your bike
Go into the rock quarry level and go into the objective in front of you fall of your bike and retry the objective you will be on the ground with your bike on you.
Jump 600 feet in the Everglades level
From your starting point on the dock, back up a bit and look to your left. Ride over to the set of jumps that are at the other end of the barges. Once in the area, ride over the jumps to your left until you come to the jump that is directly left of a palm tree. Past this jump are two landing slopes: one that is directly in front of the jump next to the palm tree, and one that is behind it and to the left. Ride over to the second slope, and face the right hand corner/side area of it. Continuously ride into this area, trying to push your way through it. With some speed and the proper placement, you should be able to ride right through the corner of the slope and ''fall'' through the ground, eventually re-spawning back onto the dock where you started out. During this fall you will also be able to string together as many tricks as you wish for an insanely huge multiplier without the fear of crashing, because when you re-spawn back onto the dock, the game still acts as if you're in the air (but be careful with the gas and brake/reverse, however, because the game also acts as though you're on the ground as well). When you're done with your multiplier, speed off into the level as you would normally. If done correctly, when your jump distance meter appears, it should read more than six hundred feet.
Performing faster rotations
While not moving, hold Square and Left or Right and press the gas (X). To make faster rotations, hold the clutch (L2) immediately before you perform this.