Since I spent my entire career writing for pay, I have lots of ideas on how to write things. Here's my advice on artist bios:
Should you use first person or third? One advantage of third is that a common use of the web bio is for other people -- such as a guild who has engaged you as a speaker -- to copy for their newsletter or flyers. One advantage of first is that you may come across as more accessible and friendly to people who visit your site. If you're writing a bio to be given to gallery visitors or included in a catalog, third is probably best.
Which situation seems to be more important or more common to you? It depends on how you plan to use the bio and what you think is going to happen as a result of it. And remember that you can have different bios for different purposes. For instance, you might write your bio differently to post on your website than to submit to a magazine to accompany an article.
How long should a bio be? I have a hard time thinking of anybody so fascinating that we really need to know more than a paragraph about her life -- at least at first glance. Sure, once I get to know you I might be really interested in your college career or your cats or your children or your world travels, but the casual observer probably isn't. Choose the details of your life that are (a) most different from the ordinary and/or (b) most relevant to your art. Omit others.
I recently read a blog from a professional gallery owner/art dealer suggesting that the artist bio is a strong selling tool, that buyers are more likely to connect emotionally with artists who have compelling stories. This guy thinks a bio should run from three to ten pages. I respectfully think this is ridiculous. Life is short. Attention spans are even shorter. I have a hard time thinking that potential buyers are going to go home, fix a martini and read ten pages of your bio before calling the gallery back to read them their credit card number. Maybe people are willing to make this investment of time before they invest five or more figures worth of money, but not in the art quilt portion of the art world.
Besides, what can you possibly say about yourself that will go on for three to ten pages? Your SAT scores and GPA? Every guy you ever dated? Your favorite books, movies and vegetables? Your net worth and investment profile? If you have the world's most melodramatic life story, then go a bit longer, but for most of us ordinary people, a page is plenty long. Probably too long.
In writing an artist bio there's a fine line between putting forth your accomplishments and appearing to be boastful. If your art quilt hangs in the Museum of Modern Art or the Oval Office or went to the space station on a shuttle, by all means mention that in your bio. If you got into Quilt National 10 times, mention it. But if you recently had work in a group show at the Caterpillar dealership in West Podunk, leave it out -- along with the 28 other shows you recently had work in. It's fine to memorialize all the shows and exhibits in your lifetime, but do it on a separate page on your website or in a separate document called the resume.
Above all, don't use artspeak unless you are represented by Larry Gagosian (and if you are, he'll probably have some high-priced ghost writer do the bio for you). Pretend you are talking to a friend of a friend, somebody you've just met. Use the kind of words you would use in speaking to a well-educated but ordinary person. Never use a word you have found in a thesaurus or have had to look up in the dictionary (except to check on the spelling).
And when in doubt, tone it down. It's better to present yourself in a modest manner and allow people to be pleasantly surprised by how wonderful you are than vice versa.