If you memorize fire arm safety rules with both your mind and your muscles, you shouldn't have any issues with your finger being on the trigger when it shouldn't be.

1. Treat every weapon as if it was loaded.
2. Never point a weapon at anything you do not intend to shoot.
3. Keep your finger off the trigger until you intend to fire.
4. Keep your weapon on safe, until you intend to fire. (with a Glock, rule 3 is your safety)