Once you are safely aimed at the backstop your trigger should be on the trigger. At the same time you are focused on a spot on the target. As the dot on the scope comes to the spot on the target, the shot should break.
It is important to aim at a specific spot on the target, and not just the whole target. Always take the shot coming into the spot.
Following through is very important, as in any shooting sport. After the shot has broken, stay focused on that same spot for at least a count of two. Also, your finger should be held back for those two seconds, any movement forward will cause a miss, pull it back leave it back.