Open Question: What Is The Best Way To Start In Sprinting?

Last Year I Ran The 100m in 12.8 seconds, which was the fastest time in my grade, but I had the worst starts in the whole team. I want to fix my starts. Can anybody give me advice and tell me if my dominant leg should be in the front in the back? P.S. I'm only in middle school so I don't have any blocks during the races.