Identify your purpose and audience. Before you get started writing, you need to know who you're writing for. The bio you would write for a personal web page might be very different than the bio you would write for a college application. Use this to make your bio appropriately formal, funny, professional, or personal.

Narrow down your information. Be ruthless here—–even the most interesting of anecdotes may not be appropriate. For example, an author's bio on a book jacket often mentions past writing accomplishments, whereas an athlete's bio on a team website often mentions the person's height and weight. While it's often okay to add a few extraneous details, they should not make up the majority of your bio.

Write in the third person (optional). Writing in the third person will make your bio sound more objective – like it’s been written by someone else – which can be useful in a formal setting (ex. for work). If the bio is personal, however, writing it in the first person will make it sound friendlier.Write your name. This should be the first thing you write. Assume that the people reading the bio know nothing about you.

State your claim to fame. What are you known for? What do you do for a living? Don't leave this to the end or make your readers guess—they won't and they may well lose interest quickly if it's not up front. This should be explicitly stated in the first or second sentence. Usually, combining it with your name is easiest.

Mention your most important accomplishments, if applicable. This is a tricky one, and might not be applicable in all situations. Remember that a bio is not a resume. Do not list your accomplishments, and only include them if they are relevant and you have space.

His 2011 series “All that and More” earned him Boulder’s prestigious “Up-and-Comer” award.

Include personal, humanizing details. This is a nice way to invite the reader to care. It’s also your chance to get some of your personality across.

When he isn’t glued to a computer screen, he spends time working in the garden, playing trivia at the pub, and trying very hard not be the worst pool player in the Rockies.

Include contact information. This is usually done in the last sentence. If it's to be published online, be careful with the email address in order to avoid spam. Many people write email addresses online as something like: greg (at) fizzlemail (dot) com.

You can reach him at dkeller (at) email (dot) com.Aim for at least 250 words. For an online blurb, this is just enough to give the reader a taste of your life and personality without becoming a bore. For a more serious post such as a college entrance bio, delve into the details a little more.

Proofread and revise. Rarely is writing perfect the first time it hits the pages. And because personal bios are only a small snapshot of a person's life, upon rereading your bio, you might realize there was information you forgot to include.

Keep your bio up to date. Every once in a while, go back and update your bio. By putting in a little work frequently to keep it up to date, you'll save yourself a lot of work when you need to use it again.

(from http://www.wikihow.com/Write-a-Personal-Bio)