Selling yourself as an author

I've been thinking a lot about the way that I present myself as an author. I haven't published anything yet because I haven't felt that my work was ready, but when I do I want to be prepared. While I know what to do when I am called to a job interview, I have no idea how to sell myself as a writer. I've tried this in the past in query letters, and been told that the query letter was great but my story wasn't. I didn't mind being told that my story wasn't great. I made a big mistake by trying to send my work out before it was ready. I think a lot of young authors do that, and at the time I was about 19. Now that my writing has matured I feel like I need to take a different approach to selling my books. I'm just not sure how to do it. I don't even know when to start, or where.