Who are you? That may seem like a simple question, but think about it. Most of us present different personae in different situations or to different people. So if you're posting a professional bio to your website, a professional directory, or a popular social media platform such as LinkedIn, you'd better customize the way you present yourself for optimal results. Here are some tips to keep in mind.
Imagine your audience. Would you use the same approach to ask for a date that you would to ask for a job? (I'm assuming that asking for dates isn't your job, of course.) Business owners or representatives need to introduce themselves, not to the general public, but to their public, the specific target audience they aim to cultivate. Think hard about the ideal reader of your bio blurb. What do you want that reader to do? Offer you a job? Check out your products or services? Recommend you to an associate? Focus on telling that person exactly what they'll want to hear so you can get the desired response.
Match the bio to its surroundings. I've been called in to rewrite employee bios that stuck out like broken teeth on the client's website because they simply didn't match the style and tone of other bios on the same page (or of the site in general). There's always one guy who insists on providing 500 words when everyone else has made do with 100 or less (or vice versa), or whose bio uses first-person address in a sea of surrounding third-person entries. Some bios may seem overly friendly in contrast to the rest of the page, while others may seem relatively dry and stiff. If your bio will be added to a general bio page, read the existing entries carefully and try to match their characteristics. The exception to this rule occurs when your bio will sit alongside those of your competitors on a directory page. On those occasions you definitely want to stand out as much as possible, as long as you stand out in a good way!)
Keep things clear and readable. A bio isn't a resume. Your goal is not to include every single detail of your professional/academic/personal life; it's to get the reader interested in who you are and what you offer, period. Ever looked at the author bio on a book jacket? In most cases, you get the least you need to know to make you think, "Wow, this author has some impressive credentials. I think I'll give this book a shot." Feel free to write a long draft, but be willing to go back and cut (and cut, and cut). As for word choices, go for clarity above all else. Impress the reader, not with the size of your vocabulary, but with the high points of your skills and experience.
Good luck telling your story -- and if you need any professional help, just let me know!