The main body includes the biggest amount of information. It is 80-90% of the whole text. There are no strict requirements, but you should not forget to use a logical sequence and correct wording. You can use the classic five-paragraph structure for your autobiographical essay if your ideas fit it. Anyway, you have to divide your writing into separated paragraphs to increase the readability of your essay. You should also create a logical connection between paragraphs. In this manner, readers will easily follow your thoughts.
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.