When you engage in combat with an enemy plane there are three weak points that you will want to hone your attack on in order to eliminate them as quickly as possible.
Cockpit:
The weakest point of any plane is the cockpit. If you hit this part of the plane you will inflict bleed on your enemy which unless they have a first-aid kit will eventually result in their death.
Wings and Body:
Firing at the the wings and body of the plane will inflict bleed and cause it to catch fire and deteriorate over time.
Fuselage (Tail):
If you hit the tail of a plane you will cause it to leak will result in the enemy pilot suffering from lower boost, turning, and breaking power. This will basically render the enemy plane useless and make it easy to eliminate.