Lots of good advise in the other replies.
I was a principal at at a fairly large independent label from 1990 through 1996 so I know a few things about the world of independent labels (though some of it may be a bit dated by now.) By the time we sold the label in 1996, we had developed a network of about 16 different independent music distributors, which allowed us to get our music in stores everywhere in the U.S., Canada and Western Europe.
Back then, distribution was certainly one of the key elements, and made our label a particularly attractive company to buy. With Nirvana breaking big through an independent label, independent distributors (as opposed to major label distributors) became a viable and desirable alternative.
Independent distribution is very hard to get these days. The 'major' independents don't want to waste time distributing a label that does not have seasoned veterans running it; that is, a label without an experienced promotion department (radio), publicity department (press), sales department (working the retailers). Of course, all these "departments" can be hired on as independents on an outsourced basis, but it can get expensive ($500 or so a week will get you a radio promoter and a publicity person.)
A good place to start is working colleges. When I was doing it, there was a trade magazine called CMJ (College Music Journal) that listed all the college radio stations and their respective play list, along with a contact name and phone number. College radio is not as regimented as commercial, and its a bit easier to get a hold of the music directors. You just call them and talk to them about your band, send them a record, and follow up to close the sale (get it on the air!) Colleges also have newspapers for reviews, and venues for the bands to play at...a kind of micro community.
If you get enough college stations to play the record, you have a story to tell commercial radio stations and press. Advertising with the press you want to get written up by doesn't hurt either. Signing bands that are ready, willing and able to go on the road was also critical. It's much easier to sell the project when the band is "coming to your town". Interviews are easier to get, as well as radio play.
Running an independent label is a bit like the "proverbial chicken and the egg". To get distribution, you have got to create a demand for your product. Creating demand without having distribution (your product in the stores) can be equally difficult (promotional entities like radio and press don't like to promote things that are not available for sale.) However, all is not lost! You can always begin regionally and put your records in the local music stores on consignment, and there is now the added blessing of selling via your own web site and other Internet channels.
Billboard Magazine has a number of trade journals available for sale (radio station listings, retailers, distributors, etc. and Poll Star (sp?) magazine list all the venues for bands to play at (at least they did when I was doing it.)
The most important part of the independent record company equation is the music + desire + dedication + determination + diligence to get it heard.
A little money doesn't hurt either.
Hope this helps.
Good luck,
Max Havoc