Write a paragraph about your birth and upbringing. Include all of the places you've lived in and, if possible, tie the affect on your acting career any of those places may have had on your acting career. If you were a part of any special acting groups or drama classes during your school years, include that information.
Include a paragraph or two about what you do in addition to acting if you are currently not acting full time. This will give your bio readers a look into your personal life and how how might affect your work as an actor.
Write about your acting credits without making a list of credits. An acting resume, where you list all of your credits, is different than a biography. Include some of your bigger roles, but weave them throughout your bio as they fit the timeline. This makes more interesting reading than creating a list, and it's more suited to an acting biography.