It's partly luck and being in the right place at the right time, so don't get too discouraged. Just be prepared for the likelihood of other players taking your kill or the torpedoes missing their target. Unless you also have the card that makes the torpedoes stronger, you'll usually want to weaken the enemy ships down to half health first with your ship's standard blasters or other abilities before you attempt a kill with RB.
If you have no cards for the bomber class whatsoever like I did for awhile, then craft that one first. There are some cards that can help with this, particularly Advanced Target Lock. Bots count too, like the objective marked Y-Wings or Tie Bombers.
For this you need to be the bomber class on Starfighter Assault, and get 50 kills with the dual proton torpedoes by using RB.
