You have learned from one mistake - that is good. One of my favourite quotes is from Bill Gates "Success teaches nothing."
One way to avoid mistakes is to learn from others. Scout out some instructors. I tell instructor-wannabes that they have to have made a lot mistakes before they can impart their experience to others.
ISPA Yachtmaster Offshore Instructor Evaluator
CYA Advanced Cruising Instructor
IYT Yachtmaster Coastal Instructor
As I sail, I praise God, and care not. (Luke Foxe)