At this point in the game, I believe the following to be core precepts to mastering the game. Don't blame the dice, don't blame the matchup - look to your own abilities and identify your failures - and enjoy the coming of X-wing SE (Did anyone notice if they made Greedo Shoot First?)
List Building (Point cost efficiency, Synergy, Action Economy, Obstacle choice, Meta Analysis)
Turn 0 deployment. (Ship and obstacle placement, understanding your opponents list, choosing the point of engagement and the role of initiative)
Attack line (How your ships move, planning for future turns and forcing the engagement)
Gauging Range (AKA spatial acuity - For Attacks, Arcs, Abilities and maneuvers)
Optimizing Action Advantage (specifically, maximizing your economy while attacking your opponents economy, turn by turn action selections)
Yomi (Bluffing, Reading your opponent, assessing your opponents skill level)
From the above, Attack line and winning the action economy struggle are perhaps the most important - Attack line and Action economy both become constrained ever further as play goes on - with more "possibilities" in the early game, and very few in the endgame. X-wing is playing chess and poker at the same time - that's why it's special, but as in the tragedy of Darth Picardus the Magnificent, - "It's possible to commit no mistakes and still lose"