When the game starts and both planes are on the ground, wait until the other aircraft takes off. Time a shot with your cannon just after it is off the ground and also try hitting it with the gun.
Try to land at the start of each round. Try to get in a sneaky hit at the beginning with a well placed cannon shot.
When you are accelerating and turning, the enemy plane will do the same thing. The result is that neither of you can hit each other. While you are doing this, release the throttle, but keep turning. You will be able to shoot them with your cannon.