Aerial combat is about energy management, when in combat you need to fly your manouvers with max power and basically fly elegant curves/loops in the air and while doing this try loosing as little speed as possible. Avoid horizontal combat, always try to gain altitude advantage over your enemy. The best tactic is to always ensure altitude advantage (online 2-3000m at least), this will enable you to to put your enemy in a situation where he got two options:
1. climb after you and risk getting shoot down when he stalls out or you turn and attack
2. dive for the deck and try to escape
If you are below somebody then you should not try to climb but dive and make your opponent follow you and make him overspeed, when he realizes that he's too fast then he will pull up and you can follow him and gain altitude in a safe position behind him.
It can be a little bit like an aerial chess game where you can force your opponent to make proper decisions quick or die.
Sooner or later everybody makes a mistake.
When not in combat set throtle to 60-70% otherwise you overheat your engine.
