Make a list of music magazines in which you would like to see your band written about. This is a useful way to help you and your band know the audience you want to reach and who you want coming to your shows. Consider adding online music blogs to your list as these are increasingly popular among music fans. Once you've got the list down, get the contact information (often found on the magazine's website or in the fine print in the magazines).
Write a press release that includes a brief description of your band, the sound you're after or genre you adhere to, and email it out to media outlets. The best place to send the press release is to your local paper, arts/music weeklies (most cities have at least one or two of these), local radio stations and local promoters. Contact student papers at local colleges or universities. Include your contact information, and mention that band members are available for interviews.
Take advantage of social networking sites geared toward musicians and consider setting up a website or blog for your band. Grooveshark, Soundcloud and Bandcamp are all excellent sites for musicians. This is a great way for people to hear some of your music and get a grasp of your sound and musical direction. Links to your site can be included in press releases and emails, which is much cheaper and easier than sending out demo discs or digital sound files.
Keep a media contact sheet and revisit it regularly. This contact list should include the music magazines you hope to have cover your band. Inform contacts of upcoming gigs, releases and other events your band is promoting. Music magazines and online music blogs are often in need of content, and most will show an interest in what you're doing, particularly if you have an upcoming release, tour or show.
Start by promoting your band to smaller publications as this builds momentum. Once your band has been interviewed and/or profiled/reviewed in some smaller sites, blogs and magazines (particularly local ones), it will be easier and more likely that larger, regional and national publications will be interested in you. Keep this in mind and keep at it. If you are dedicated to your band and to lots of performing and promoting, you are more likely to generate interest among writers and publicists.