Get in Close
Tommy McGuire, an ace of the USAAF in WWII, once said "Go in close, and then when you think you are too close, go in closer." The guns on your plane simply are not accurate at long distances, and even if they were, they will lose so much penetrating power as they travel that a hit would be nearly useless. Never fire on an enemy plane that is over 200 meters out, and try to get even closer before you fire in order to deliver the maximum damage your weapons can put out.
Lead your Target
Planes are not stationary targets; they will be dodging and juking all over the sky in an effort to keep your bullets from destroying their fragile bodies. Never shoot straight at an enemy plane; shoot in front of an enemy plane to make sure your bullets and the enemy plane are in the same airspace at the same time.
Attack from an Angle
A near-miss is still a miss. You will never have a worse shot than when you try to shoot an enemy fighter from straight-on or straight-behind. Their profile is as thin as it can be, and your bullets will likely pass over or under the wings. Instead, attack from an angle -- above, below or from the side -- to give yourself the largest possible target
Watch your Convergence Angles
Convergence is the point in space where the hot lead poured out by your machine guns intersects. Your machine guns do not fire straight forward; they fire slightly at an angle, and that angle converges at a fixed distance from your plane. Take the convergence into account when you fire on a plane; if you are too close, your bullets may pass to either side of your intended target. Watch what your bullets are doing and correct as needed in the cockpit.