1) Fly a fast aircraft
Nothing helps you stay alive better than an aeroplane with speed. Speed allows you to disengage from a disadvantageous fight and survive to RTB. It also allows you to dictate terms of the fight. You can choose to engage when you have the speed advantage, and can ultimately dictate the fight.
However fast aircraft generally have poor turning performance, (unless flying the 109 or Spitfire XVI), so play to your strengths.
2) Never fight fair
However sportsmanlike or "combat orientated" the game-play may seem, NEVER, engage unless you are certain of victory. If there is more than one, fall back to an area where friendlies are flying, this allows you to shoot the enemy off their tails and allows your friendlies to do the same for you. Also, if the pilot is better than you, the 1st point about speed allows you to disengage and survive and perhaps turn the tables later.
It is also worthy of note that use of altitude is your best option when adopting this method.
3) Don't HO.
Head On attacks are generally a case of MAD or Mutually Assured Destruction. You will both die if you HO. Unless you adopt a HOing aircraft such as a 190, NIKI, Typhoon,110 or 410. These attacks are generally inadvisable. Always avoid the HO by diving underneath, and then pulling into an Immelman or High Yo-Yo. To position yourself behind the enemy.
4) When in doubt, disengage
If at any time your situation is beginning to look grim. Disengage and fly home and or climb to altitude away from the fight.
Hope this helps
