Checking your own 12 thru 12 is all part of SA (Situation Awareness) which is something you have to get REALLY good at and do it often. Its called "paranoia" !!! Complacency, while flying, is a sure fire way to get whacked every time you go up.
For every plane you get into, prior to takeoff, make sure that you adjust ALL your views so that you can get the best available 360 degree horizontal and "up" views that the plane will allow. Once the views are set, you will not have to adjust them again. Also, make sure you set your gun(s) convergence on any new plane that you jump into. Convergence is also a setting that will be remembered.
Without good visibility and due diligence on checking all areas around you, you will be a victim of more "Boom and Zooms" than you would care to count.
While most countrymen will give you a check six, you cannot always depend on it and sometimes you will get a "Check Six" the second after the bullets start ripping your plane apart.
Anytime I get a "Check Six" I make the most violent maneuver that the aircraft will handle and almost always, like popey, I will do a Split-S immediately (altitude providing) or a defensive barrel-roll or anything that will get me out of the jam. While pulling the escape maneuver, I then start switching to all rear views to see which direction the enemy went and sometimes they make the wrong move and you can reverse rolls.