Always treat every gun like it's loaded, even when you know it's not. Practice muzzle awareness (where the gun is pointed). Never put your finger inside the trigger guard until you're ready to pull the trigger. Keep the safety on until you're on target. Finally, know what's beyond your target. I shot myself in the knee loading a 9mm years ago. Easily preventable accident. I was sitting on a ledge with my leg propped up. Loaded the mag, pulled back the slide, hit the slide release, and POW! Looking back, I'm 99% sure I had my finger on the trigger when I released the slide, allowing the firing pin to strike the primer on the bullet being chambered.