Short biographies are used to convey basic information about yourself that readers may find useful. A bio can be used as a description on a social networking site, a means of qualifying a piece of your work or as part of a job application. A short biography shouldn't be more than one or two paragraphs, and it shouldn't be very difficult to write. The trick is knowing which details are important and conveying them in the briefest manner possible.
Examine the context of the biography. What is your audience interested in reading? If you're a published author, they will likely want to know what writing you have done and how long you have been doing so. If you're applying for a job, the reader will want to know your work experience, the types of jobs you've held and perhaps the education you've received. Make lists of these elements of your biography. Be sure to include any awards you've won and any notable projects on which you've worked.
Considering the lists you've written in step 1, narrow them down to which details pop out the most. You're looking for highlights of your life, events and accomplishments that really shine and that provide as comprehensive a look at who you are in as short a space as possible. Pare the list down to a few key details---things that can be easily described in a sentence or two---and discard the rest.
Think about how much of your personal life should be included in the description. These facts can include where you grew up, how you spent your formative years, where you currently reside and information about your spouse or children. Maybe include any hobbies or passions as well---specifics that humanise you a bit and help the reader relate to you a little better. Determine how pertinent they are to the context of the biography, and write them down in a list just as you did in step 1.
Examine the list of personal information. Select only one or two details at the most, and discard the rest.
Write down the details you have chosen in a few paragraphs, constituting an overview of your life. Start with the most important detail in the first sentence---for example, "John Smith is an award-winning author with over 10 published novels to his credit," or "Jane Doe has worked for the past 20 years in the field of biochemistry." Use that statement as a springboard to other details that bolster your reputation and underscore your pertinent achievements. Finish the biography with a single sentence or two dedicated to your personal life---for example, "He lives in Medford, Oregon, with his wife Rebecca and their two children." The end of the biography should also include any contact information, if applicable.
Edit and polish your biography to eliminate anything you feel is impertinent. The briefer it is, the more readily people will read it, but it shouldn't be so brief that you sound bland or uninteresting. Practice makes perfect in this regard, and if you work at it, you'll soon get a sense of the precise balance you need.
Biographies should always be written in the third person. Write as if you were someone else describing yourself, using "he" or "she" rather than "I."