Talent, hard work and luck as others have said are important. Also important is ambition.

I believe that many of those who "make it" (however you define it) are in some way driven and often succeed in the more commercial sense because of their desire to succeed - their ambition.

I had an interesting discussion on this theme with some friends last weekend. It came out of a comment on one of the performers that evening who has a fine voice is no mean songwriter and we were wondering why some succeed while other, equally talented people don't. They cited an example of a friend whose ambition was to be famous and she had chosen folk music because she felt it was less crowded than other musical genres. In effect she was in folk music as a means to another end rather than for the music itself.