Skill is shooting where the enemy plane/vehicle will be, and not hoping for a hit.
Skill is maneuvering your plane by reflex, not by thinking about what to do next.
Skill is not having your confidence shaken when faced with more than one adversary at a time.
Skill is flying and maneuvering your plane while looking somewhere other than your front view.
Skill is making the red guys react to your tactics, not you reacting to theirs.
Skill is firing your main gun, and turning to the next target because you know your round will hit what you were aiming at.
Skill is jumping competently from weapons platform to weapons platform and giving the enemy hell the entire time. From plane to vehicle and from field guns to ships gun/shore batteries. Non-stop combat capable.