You usually want to flap before a gate, with Chirpz being slightly above the height of the lower pillar. Usually flapping inside of the pillars will result in a death. When the gates are skewed to the left, you can afford an early flap out of the gate; whereas when it is skewed to the right, you usually have to allow a bit of freefall to avoid hitting the top pillar. Take care when the difference in height between successive gates is large. Also if you're trying to reach a high score, it is recommended to manually restart rather than waiting for the end cutscene to finish (unless a highscore has been set).