Listen to this great description of how one listener uses and enjoys iMix selections from the Apple iTunes Music Store. People in America used to use radio and mixtapes for that kind of experience, but now they turn to other listeners online.
So here's one suggestion to boost sales of your music while growing your audience.
Think about the ways that your current listeners have told you they use your music. Has a song of yours gotten someone over a break-up? Do people use your songs for working out? Anybody get a speeding ticket listening to your stuff?
Think about the activity that someone might be doing while listening to one of your songs. Then, build a playist of familiar music *around* your song. It's a great way to slip your music unsuspectingly into the iPods of new listeners.