Talk with the autobiography subject or subject's representative about the scope of the work. Know whether the project you ghostwrite is for a book covering an entire life or limited to a certain period, such as childhood.
Research your subject to see what others have already written about him. While a ghostwriter should check the accuracy of the information, the information might also provide you with a list of questions.
Interview the subject to get a complete picture. Ask questions generated by your research, but be prepared to go off on tangents. Some unplanned conversations make interesting material for an autobiography, but don't hesitate to steer your subject back on course.
Tape interviews for accuracy of information and for the quotes you can use in the autobiography. Check your facts for accuracy. A ghostwriter sometimes needs to talk with interview subjects again to clarify a point or check for accuracy.
Talk with other people who knew the subject. Not only will you have a more complete picture of the subject, but you'll also get more information about shared events that took place.
Familiarize yourself with the concept of voice as it applies to writing. Voice varies according to author and project, but it's a distinctive way of telling a story. In the case of an autobiography, a reader should recognize the voice as that of the autobiography subject.
Ghostwrite an autobiography by putting yourself in the subject's place. Think like your subject so that you'll sound like your subject.