Its very difficult to get a hit on fighters, ties especially.  Like slimshiesty says you have to hit them in the right spots, but also be sure that you have a low ping.  If you don't it will be easy for others to shoot you, but not vice versa.  A good strategy is to find an enemy, don't fly head on wait for him to pass you then come up from behind.  Line up your shot and hope he doesn't turn in time otherwise you'll be stuck in the endless circle dogfight.  Its all about the ping when dogfighting.

Perhaps the devs could increase the hitbox on the ties, since its very easy for a tie to take out rebel fighters (they're only advantage is that they have more armor, but this is canceled when a tie is nearly invincible)?

all about angles, with the right angle you get deflections, the other right angle you get hits.
In other words try to get in front or behind them to ensure a kill..or death, if he hits you first.