There are many iTunes promotion companies in existence, who understand iTunes music marketing and how to get people clicking and downloading songs. iTunes is an incredibly popular music platform, particularly because of its compatibility with Apple products, so getting your music high up on their list could make you a lot of money.
Whatever your music genre, you could benefit from using one of these promotion companies, who will tailor their advertising and strategy to your music, rather than delivering a blanket service to everyone.
Most of these production companies will work on previously released songs as well as new pieces, allowing you to create a buzz around all of your productions, and sustain sales on a song which has promise. There are other strategies which you could try to get your song seen and heard; for example, advertise on iTunes’ front page, which will be seen by hundreds of users when they sign into the store with the intention of spending money.