Following some of the suggestions from the php|architect folks about getting your ideas accepted at conferences, Lorna Mitchell has posted some of her thought process behind coming up with a good conference bio.
To get to this point, I started with a list of things I should include. My job, my blog, my community activity, my technical interests. [...] I then turned my points into sentences, and emailed the result to a few people to read. [...] I always take this approach even when I know I'm probably making a hash of it, if I'm asking for someone's input, I take the time to attempt it myself and send them the result.
She also notes that proofreaders are always a big help, catching some of the small things that you might gloss over and could make your bio. You can get a few other ideas and examples here, here or here.