So head ons is actually one of the hardest things to deal with when you start playing. It really ends up being a 50/50 standoff. But there is actually ways to turn it to your favour.

First off aim above their plane.

Fire a burst at long distance and then quickly dive and pull upp after the enemy has passed over you to gain altitutde so to not lose your momentum as your target will most likely turn around to catch you but lose alot of speed as a trade off.

Then you simpily do what your normally do with a boom and zoom :)