h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

If want to form or join a band advertise your skills... and advertise them EVERYWHERE: music shops, local message boards (both online and physical), music magazines, even your local newsagent may be willing to display your ad.

You should also make sure you make the intent of the advert perfectly clear. Mention what instrument(s) you play, what music you'd like to play, which bands influence you, whether you have had any previous gigging exprience... and don't forget to put contact details down as well! Steer clear of anything which makes you seem snobbish or hostile about certain types of music as it may put people off.

I absolutely agree. Just some extra suggestions:

1) As with all advertising, make sure you are consistient. Use the same typeface, images, proportions, layout, and color. If a person sees one nice poster, they will swear to remember where the concert is, and proceed to forget everything during their converstion with the cute girl in the phone booth two meters away. If said person later hears a PA announcement of the concert exactly as the poster said it, then goes home and sees the same poster on their favorite website, they just may do some mental spring cleaning and remember to show up.

2) Put aside your musician ego and face facts: Musicians might go to concerts for music. Normal people don't go to concerts for the music - they go for the party. Music is an excuse for people to get together and dance or chat or any of forty-two other activites; good music is only a bonus. This is true of every genre, in every time period.
So when you advertise, emphasize the event instead of the band. Convince people that they're going to have fun. If you want continued success for your band, follow through and provide a dance floor, food, an atmosphere where people can hang out. Only ever let the band be half of the feature. A benefit concert is a great way to start.

I have never been in a band outside of school concert bands, but a group which has sprung to fame in my area over the past year or so seem to have done a few things right. To begin with, they played a lot of gigs for free at local schools, which got everyone interested. They don't play covers (or, at least only very sparingly), so most of the material was stuff people hadn't heard before. This got us all excited, because here was a band playing things we didn't already know as "popular music" in a way that got us all dancing.

Following that string of gigs, they gave a performance with some other local bands and - this was the exceedingly popularity-boosting move - gave out free copies of their cd. Worked a treat! Everyone played it, and played it to their friends, and now they've played with some bands that are well known internationally. It probably helps that they are all quite good at their instruments, and have a charismatic lead singer, but the way they set about getting popular really worked - interacting with school students meant there were a lot of people who knew about them, and had actually met them.

I'll go with what Gullibility Personified said. My friend started a band and is now playing at Glastonbury and the like.

When they first started they played and played and played. There was no way they were going to perform in public without being prepared. It gives your audience a real downer if you aren't any good and you'll quickly find that nobody will let you play in their venue.

The next thing they did was to have new songs AND a few covers. Some people might go at this, but it's well worth having some backup pieces to play. And of course everyone likes to be able to dance around to things they know. Pick pieces that reflect your style of course. Friends with a ska band chose to play the 'Arthur' cartoon theme and 'Oliver's Army' which went down well. Having a complete change in pace can be good, but it depends on your style and ability for different types of music.

Then as GP said, play anywhere and everywhere! Play at schools, pubs, town halls, churches (if you're stuck for somewhere else), parties, society functions...anything you feel you can be associated safely with.

Playing at small festivals, town events, contests and the like are a good way to get the general public to see you, even if you actually have to pay a fee to be in it.

Oh and playing your own instruments is a big top must. Obviously with bands, pieces can often be learned by heart and tinkered with along the way. You aren't expecting other people to play your things so being able to read music is not a must-unless your main writer uses it.
Short-cuts...erm learning bass guitar can be a short-cut for someone not good at remembering loads of things. They give the good solid dum-dum-ding-dum beats underlying everything and pieces can often only need 3 chords for the bass.
It's important to have a good drummer though. A bad one flips the rest of the band and one that won't practice is just as bad.