The first step in writing a biography is choosing someone to write about. There are no rules for selecting a subject, but it will make the process more enjoyable for you if you pick someone you find interesting. Take some time before you commit to be sure the life you are detailing is one that will make you want to get to work.
Since a biography is based on true events, it is imperative that you do proper research before you start writing. Look through books, magazines, newspaper clippings and on the Internet for reliable information. Be wary of online sources, however, as anyone can post information. If possible, interview either the subject himself, or someone who knew the person. Also, try to explore the world he lived in if you can. Visit restaurants or coffee shops or book stores he spent time in to really get a feel of what his life was like.
Learn everything about your subject's life, then select one aspect or time period and focus on it. It could be her college years, or first years in a certain business or childhood. Try to find an angle that has yet to be explored.
Your outline is where you organize your thoughts and get all your research out on paper. Write down all of the elements you want to include in the biography in chronological order. You can make it in point form, or sentence form or whatever will make it easier for you to translate later.
When your research has been done and your thoughts have been organized on paper, write the biography. Don't over-analyze everything, just write. If you feel you aren't quite ready, write it anyway. Many writers procrastinate at this point, but the only way you will ever have a finished biography is if you start.
The editing process is where your biography will really come to life. It is the time to remove any impurities and unnecessary elements. Read your biography out loud to yourself and to someone else. Look for a logical flow of information, check your grammar and double-check your research to be sure all information is accurate.