You, and what can be done to personally record your own history so far before it starts to fade or get fuzzy in the old noggin. Writing either on the computer or by hand is an obvious first choice, using a computer makes the task of editing a lot easier. While working on large projects, it's also a good idea to save incremental versions just in case the current file goes bad. If writing isn't for you, there are other options. Sit down in front of a cam corder for a couple of evenings, recording directly to a video cassette recorder will make for a higher quality recording in most cases.
Audio tape is also another possibility and using a better grade of tape is always a plus.
It might even be fun to sit down with family members and take turns interviewing each other if for no other reason than spontaneity. You'll be tempted to edit out the fits of laughter or other outcroppings of emotion that come up along the way, but keep these parts intact. They are often contain the best material, think about how nice it will be for future generations to know what someone's laughter sounded like. Your Life Story will provided the motivation. Nobody knows your story better than you do.