Take a step back to reflect. You're chronicling your life lessons, but what have you learned from them? Relay your intentions, desires, feelings of loss, feelings of joy, the wisdom you've gained, and other inner thoughts from time to time throughout the book. Taking a step back from the action of the story to reflect on what it all means is a good way to add depth to your autobiography.
While you might not remember every detail about a certain event, I guarantee someone who was there does remember. Asking family and friends for ideas or details of a certain situation can give you a completely different perspective of the event or time in your life. That perspective might prove to be invaluable in your writing. Be prepared; once you get a group of family and friends together to reminisce, you will be shocked at how quickly the ideas come and how one idea can spark another and another and another.