Movement
Take note of the green lines on the track. They reveal when you should flow or release. Usually you should flow at downhill slopes. Release at inclines or any type of upward areas in order to keep your speed. Practice getting the proper timing for perfect flows. Repeatedly tap the "Flow" button at the start of a race to begin gaining momentum. Also do this at the face of an incline. Tap "Flow" to have your biker pedal faster instead of just waiting for him to pass up the hill.
Tricks
Perform mid-air tricks to fill the adrenaline meter. When full, you will receive a temporary speed and jump boost. Try to perform as many tricks as possible, even without ramps to launch from, by using little bumps on the track. Make sure you finish your trick before landing or you will lose speed. Tap the "Flow" button just before landing to get a smooth finish and keep your speed.