How do I learn from an accident to avoid future ones?

It depends on whether it was a preventable accident or not. If it was a preventable accident, then think of the ways you could have avoided it. For example, suppose you approach a yellow light, and you suddenly brake, but a guy from behind rear ends you because he was tailgating you. In this scenario, you are not considered at-fault, however, it it preventable if you glance at your mirrors periodically. This way you would have seen the tailgater and perhaps chosen to drive through the yellow light. However, you can't really derive techniques to avoid all accidents.