Sell the idea of the label itself. Brand your record label. Create a packaging and visual style that sets you apart from the rest. Sub Pop, the original home of grunge bands like Nirvana and Soundgarden, created a distinct visual style with the use of Charles Peterson's striking black and white photography that essentially sold the idea of the record label to music listeners. Do the same in terms of your label's music. Make your label's sound just as recognizable as the artists, as Motown did with its lush string arrangements and catchy songs.
Network. If you're at the point where you feel like you can run a successful independent record label, you should probably already have an extensive list of contacts in the music business. Maintain a database of everyone you know. Talk to the bands you work with and have them recommend your label to other bands and music listeners.
Buy ads in publications relevant to your record label. If you run a heavy metal label, for example, buy half- or full-page ads in magazines that feature heavy metal bands like Decibel, Kerrang or Revolver. Buy advertisements in magazines that don't necessarily focus on the genres your labels represent but might appeal to people interested in heavy metal label, such as tattoo magazines.
Seek out resources that list record labels like Ian Bessler's Songwriter's Market books, which contain lists of record labels, their genre and how they accept submitted materials. Contact the editors of these types of resources and ask if your label can be on the list.
Create a website. Ask other websites, including labels, merchandise companies, studios, etc. to link to your website. Social networking sites allow record labels to sign up under musician categories. Join them all.
Promote shows that feature the artists of your label. Advertise it as a night of "folk-rock" or whatever genre your record label works with. Fans might come by to see an artist they already know and get into other artists on your label.