The introduction to an autobiography sets the stage for the life story to follow. As such, you could use several different approaches in writing your introduction.
If the autobiography is going to be strictly chronological, the introduction would set out the initial facts. Ex: I was born on Jan. 1, 1990 at 2:23 AM. My parents knew, from my first screaming breath, that I was going to be a night owl and a challenge to control.
A flashback technique could be used if you wanted to introduce a highlight of your life, then go back and tell how it came to pass. Ex: As I strode to the podium to deliver the valedictorian's address at Commencement, I thought of all the nights spent studying, all the parties missed due to assignments I was polishing. All the work was worth it at that moment. It started in kindergarten. I got a gold star for every letter book I completed, and I loved those stars.