As is the fashion these days, most guitarists have constructed and posted websites.
Currently, there are over 750 such sites (including mine) posted on worldguitarist.com - under the 'artists' section. All of them have 'bios' or 'biography' or some like section.
Through exhaustive research, I have come up with a model bio any guitarist can use - simply insert your name and you have an instant bio
Opening and the early years
(Your name) is one of the most (choose one: exciting, sought after, desired, admired, reviled, awesome, fantastic, cute, mediocre, up-and-coming, over-competed, under-appreciated) artists of his/her generation. Born in (year of birth) in (Country of birth, unless born in the US, then state and city - as if that weren't the height of American myopia), he/she began his/her studies of guitar at age (as low as possible - one always wants to project child prodigy status; though, some have tried the early twenties, as if to say, 'hey, I got this good in just a few years', never, though, put a date in your teen years). Over the years, (your name) has studied with some of the luminaries of the guitar world including (teachers - don't be afraid to pepper the names of your actual teachers with those whom you took a 15 minute, unsatisfying, forgettable master class), among others.
Competitions and Performances
Between (year) and (year)*, (your name) was a top prizewinner in many international competitions including: (European City) International Competition, Prix de (Belgian or French City), and the (number) Annual (Acronym of local, state or international musical organization) Competition, among others.
(Your name) has given World Premieres of works by numerous composers** and has been a featured performer at several international music festivals (as noted in the note to the above date range, one wants to be sure to show a progression from student to competitor to recognized artist - and this sentence does it beautifully), among others.
As a soloist, (your name) has appeared with the (small town USA) Symphony, (heretofore unknown European) Symphony, (exotic sounding South American) Symphony, and (former Soviet) Symphony, among others.
What you are doing now
While concert tours take Mr./Mrs. (your last name) to such locations as Spain, France, Canada, Mexico, Southeast Asia and New Zealand, (your name) is also a sought after teacher and currently (heads the department, teaches, hangs out) in the guitar department at the (University, Junior College, High School Conservatory of your choice), among others.
*Be careful with this date range. One wants it to reflect a compact period of time in which you took the guitar world by storm. If the date range is too long, it begins to look a bit desperate.
**Never name the composers unless you are sure people know who they are or if they have had some music in the movies (if so - mention the movies). Unlike the names of competitions which have exotic locales and official titles which will elicit in your reader visions of cities and hallowed institutions, unknown composers will only baffle your reader and make them feel as if they are not 'in the loop'.
The above bio should work well for any guitarist. Feel free to add pertinent information about recordings and publications and be sure to put a picture next to the bio (I'm a big fan of the 'peaking-out-from-behind-the-guitar-neck' photo).
A note about the origin of the bio
Before computers, one attended concerts at which one would see performers perform a selection of pieces. In order to formalize the structure and to give the audience a better feel for the flow of the concert (and also when to clap) a 'program' was created which listed the piece. One assumes that concert promoters and impresarios, in response to the proliferation of artists that were really quite good but wholly unknown to the audience and the propensity of the audience to arrive too early decided one needed a bit more to read and in response created snippets of text about the artist (bio) and perhaps some tales - usually apocryphal - regarding the pieces (program notes). As is the way with such things, artists (or their management) decided that perhaps they could do a better job of the former and local, out-of-work history professors could do a better job of the latter, thus leaving us with the quite purple quality and prodigious quantity of current material one finds in the modern program.
Through the foregoing, we have trained our audience to expect a bio.
But there is a problem with the current state of things. The bio has become a forum in which we, for want of a better phrase, 'toot our own horn'. And to appropriate a Margaret Thatcher maxim: - Being a great guitarist is like being a lady. 'If you have to tell people you are, you aren't.'