I  have not the slightest clue, I remember reading about the offspring and they had the benefit of a large radio station in their hometown that was syndicated in some way. This in turn made their music available to other stations who started playing their single - sales went crazy.

Dave did perpetual touring locally and sold independant cd's at his shows. He also encouraged recording of his shows and asked his fans to pass out as many copies as they could to spread his music. Basically giving out free music and promoting himself yet it cost him nothing just like providing MP3's of music online. Word of mouth goes a long way. Then Dave went greedy and now does not allow recording of his shows even though that what got him where he is. Realizing the money to be made in live recordings, hence the what seems to be yearly live show release from him.

This is the same thing the Clarks did in PA. They tour constantly and have released I think 5 cds independant (close to a million sold)before getting a deal. Now they are playing 9:30, roseland, and TLA. All through touring and word of mouth.

The group Fuel used to play in harrisburg 2 nights a week and had a huge following. They put on one hell of a cover show and over time had quite a list of their own material before being picked up by Sony. they worked their asses of and played every friggin night.

So, I guess their is no real method, just hard work and luck 

Later- Jason