Heya, Happy1!
The key to good gunnery, above all else, is practice. Don't think of it so much as an equation or various rules of thumb. Thinking about shooting... computing lead in your head, using gunsight markings, determining relative speeds, etc... can lead to hesitation and inaccuracy.
It's to the point now where I find that I think very little about aiming, and in fact I had to ponder awhile about what little goes through my mind when I responded to Roscoroo. This results from practice and years of experience where I get a "feel" for the correct lead and take it.
That said, there are a few techniques that I'd recommend for improving gunnery. First, turn off your tracers. I can't stress that enough. Too often players, even vets who've been playing for years, fall back on tracers as a crutch. They walk the tracers to the target rather than choosing the correct aiming point initially; this wastes ammo. Turning tracers off forces you to actually aim using the gunsight.
Second, get in close before opening fire. I set my convergence to around 250-275, and I rarely open fire past 300 yards unless I'm trying to pick off someone extending away from me on a failed boom and zoom pass. Firing at your convergence range maximizes lethality, and firing in close increases the lethality of each gun. It's entirely possible, for instance, to nab two, three, or even four kills with a Spit V's .303s once the 20mm cannons run out simply by getting in close and firing the machine guns at convergence.
Last, take good shots and avoid bad ones. I tend to prefer deflection shots rather than straight six shots since they provide me with more of the enemy plane to hit. Very simply, the more area an enemy provides you to hit, the more likely you are to hit it. To that end, I prefer maneuvering so that I have at least some angle while shooting rather than taking pure six shots.
As for gunsights, I just use the default and always have. I've never seen the benefit in custom gunsights, but mileage varies from player to player. You may find a gunsight that helps your aim considerably, so don't rule it out.
Hope this helps!
-- Todd/Leviathn
