Weave in themes. Use the major themes of your life as a way to tie stories together, connecting your past and your present. Aside from the central conflict, what themes have followed you throughout your life? A fondness for certain holidays, your fascination with a certain place that you visited over and over, a certain type of guy you've always fallen for, a rich spiritual life you fall back on again and again. Bring up the themes every so often to help form a cohesive picture of your life.
Create an outline or a graphic organizer of the major topics and ideas you want to cover. For example, you might make a time-order chart -- a chart with event blocks to organize events chronologically. Or, you might draw a cluster web -- a diagram with connected circles -- to divide your autobiography into sections, such as one for relevant background information, one for life-changing events, one for special memories and one for goals and dreams. Focus on reasons why specific events, situations and circumstances were important to you and how they made you feel.