1.) Divide the Bio into three different categories ==> Before Canon, Intro to Canon, and After Canon. If you want, add "Trivia" for bits that you want to include, but don't want in the history.
2.) Create different subcategories within those main categories. ==> For example, for Sinn's bio, his Before Canon was divided into "Pre-Rebellion" and "Post Rebellion"
3.) Work on the parts that you want to work on first. Don't work from beginning to end because then you will get stuck. Work on parts you know for sure, and then go back and do the other parts: you'll usually find your inspiration for those parts later.
4.) If you come up with the background first, tie it into what happened in the present: it should have a major impact on the characters life.
5.) Bold names that are important to the Character you are writing about: It helps to point out that they are a major part of their life, and that they will be recurring constantly within their story.
That's about it .^-^ T