I own the starter set, and try to play now and then with my brother.
I wish there was a play by play walkthrough of a normal regular match, so that way I kn ow what I'm doing. I usually lose as the X-Wing and win as the TIEs.
I was looking into buying the Decimator soon, though, as its description and abilities appeal to me.
Some pointers for flying as the X-Wing against the TIE Fighters in the Core Set ...
Try to get into range 1 of the TIE Fighters so that you get an extra attack die (four dice total), which helps counter their three agility dice.
It's almost always a good idea to use your focus action (as opposed to using target lock) after moving. That way, you can spend your focus token to make your attack better, but if you don't roll any focuses, you can spend that focus token on defense.
Target locks only help you offensively, not defensively, so they're not quite as flexible as focuses. Best time to target lock is when an enemy ship isn't within your firing arc but it's close enough, within range 3, to target lock it. That way, when you eventually
do have it in your firing arc on a later round, you can have both a target lock
and a focus, making it very likely that you'll do damage. Remember that unspent target lock tokens don't go away at the end of a round like focus and evade tokens do.
Try to set up your X-Wing at the beginning of the game so that there is a patch of asteroids between you and where the opponent set up his TIE Fighters. Then try to lure him into the asteroid field (do some koigran turns back and forth for a couple turns, perhaps) so that he has to split up his fighters as they go around rocks and hopefully can't both shoot at you at the same time. Try to focus on one TIE Fighter until it's dead, don't switch between the two if you can help it.