I cringe at having to describe myself or write my own bios. No matter how casually an email, site, or form says "introduce yourself, no pressure", I shrink back. How do I convince myself that other people find who I am or what I do interesting?
I found myself asking this question a lot this past year, probably because I've written myself quite a few bios in the last year. Conference applications ask me who I am, social websites want me to fill out my profile, and social and professional networking has me introducing myself over email. I'm often uneasy about what to write, so I draft my bios in emacs and copy them over when I'm ready. As a result, I've ended up with a copy of every bio I've written in the last year. This turned out to be a happy accident - having copies of previous bios makes writing a new one a lot easier for me.
When I can look back at old bios, I benefit from having words at my fingertips to reuse when appropriate. When I see that I included something about me in a previous bio, I feel more confident that it's something worth including instead of something that isn't good enough. When I reread old bios, I remember what people told me worked well and what could have been better. (Keeping feedback nearby would be handy, too.) But mostly, when I see that I've written successful bios before, I feel confident that I can write a good one again.
And once I've written a new bio, I ask a friend to read it.