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.