The main points have been covered with the 'nose-up' fighter style.
Beware of this, though, it is not always the right answer. The 109 G2 and G6 will not have that climbing advantage over later mark Spitfires and a few other aircraft.
You will quickly find this out for yourself, though.
Generally, what the 109s cannot out-climb or out-run, they will out-turn. So fight to your aircraft's strengths in the given situation. That goes for any aircraft.
I like to have my guns in very close in the 109. I have my 30mm cannons at 200 yards and 20mm cannons at 300.
I never take gondolas either. I have in the past and it does work, but if you want to get down and dirty in it, you'll be shooting yourself in the foot with gondolas.
If you're looking for that extra fire-power of the extra cannons... Fly a 190, they will stay faster and are easier to control at high speeds.
My basic rule for all German aircraft is to fight in the verticle, use climbing turns and loops as opposed to diving and flat turns. This will also help you retain your altitude in a fight and help you live longer in a big fight.
Also, I consider the 109 to be one of the worst BnZ'ers in the game.. Unless you're 'Johnny on the spot' with the trim wheels, the 109s become a handful at higher speeds. In the same situation a 190 of any model would perform better. All models of 109 turn quite well so don't be affraid to mix it up. Just do so with climbing turns rather than flat ones.
Don't be affraid to get fast and stay fast in 109s... just don't rely on it as a strictly BnZ aircraft. This is one of the main reasons I prefer the 109 in AH. You CAN get into a dogfight and fight to a stand-still against pretty much anything and still come out on top if you do the job right. This is not the case with the 190s. They can also dogfight pretty well if you know your business but a 190 will always lose to a 109 in a equal situation, equal pilot fight.