Ask yourself what it is that you want to do with your music. The clearer you are on that, the easier it will be to find others who are on the same wavelength. This is true even if you aren't sure, as there are plenty of people online who would simply like to jam and see what happens.
Look at ads that are placed online. Many local musician magazines have online versions of their publications. Plus, check your local Craigslist music pages as well. Sometimes, all you may get is a phone number, but they may also have an email address. Either way, your online sleuthing will lead to contact with others. Most importantly, however, take the time to look at every detail of the ad. Most who list online are specific about all aspects of who they're looking for, your fashion sense and partying proclivities included. Look beyond the music specs and ask if you would fit in on all levels.
See if the people you've found have an online music profile, either of themselves or of a band that they have been in. The more you know, the better off you'll be. For starters, it'll lend an air of legitimacy to them, i.e., "yes, they're for real." Plus, it will be a resource for you when it comes to getting an idea of what to expect if you agree to meet up.
Learn what the first practice will entail, once you've agreed to meet up. A lot of bands have easy access to their tunes online thanks to the wide availability of affordable home recording equipment. Do they want you to learn their tunes? Or would they prefer to play a few mutually liked covers to break the ice? Either way, if you do indeed have a dead-set vision for what you wish to do, avoid those who "just want to jam and see what happens."
Place an ad for yourself if all else fails. As mentioned, many existing bands looking for the last piece of the puzzle have impossible criteria. For example, you may like to enjoy a beer or two at band practice. You then find what looks to be the perfect band, only to learn that it has a zero-tolerance policy with alcohol. Take control and advertise yourself. List everything about you, your music and how it relates. Don't write an entire bio, but give the band an idea of what it means to be in a band with you.