Autobiography is a form of nonfiction that tells a story -- or stories -- from the life of the author. Even though autobiography is different from memoir in that it is not always reflective, it still should convey at least one theme. And just like in an academic essay, your introduction has to hook the reader and express your theme, otherwise known as your purpose.
Identify Your Purpose
Before you can begin drafting you need to understand exactly what you're trying to convey. You're not merely recounting some events from your life; you're telling a story so that your reader will be able to extrapolate some greater significance. What's the point of your story? Are you telling a story of overcoming adversity to communicate the idea that perseverance is the key to success? Are you saying that love conquers all? Is there no place like home? Identify your purpose, and then you can work on how to illustrate it.
Tell a Story
The best way to hook a reader is to tell a story or anecdote that demonstrates your purpose. Don't preface it with philosophy, just dive right in at the heart of the tale. This way you will captivate your audience so they will understand your purpose without you having to state it. If your theme is that families need to stick together, show it in your introduction, or better yet, tell a story that shows what happens when families don't stick together.
Trust Your Reader
As a storyteller, you are responsible for giving your reader just enough information so that she can make inferences about the characters and plot without you having to tell her every little thing. This means you should only give significant details in your description, and stick to the facts of the story. Readers are smarter than you think, and can solve narrative puzzles quite efficiently. Let reading be an active process for your reader, meaning one in which she participates actively as opposed to simply receiving your written information.
End With Exigence
As with the example of telling an opening story about when a family doesn't stick together, you want to end your introduction in a way that the rest of the story needs to be told to really complete the story, to deliver the message and a satisfying reading experience. Your introduction is just that -- an introduction. You are whetting your audience's appetite. They've seen what happens when a family acts selfishly. Now you can deliver the longer, deeply satisfying story of what happens when they do come together.