Do not go on the blue boost that go around the edge of the track. They send you flying up high into the air, and then give you a boost when you land. If you go too high, it would have been faster to stay on the ground. Usually these boost are out of the way and force you to take a wider turn, so it is faster to stay on the ground and take a tight turn.
This picture is on Maple Treeway, and is also an example of what not to do if you want a faster time.
