There was an interesting post at the Editorial Ass blog recently that you can read here:
Want to build a name for yourself (especially online) and make yourself and your manuscript more interesting to potential agents and editors? Moonrat explains how to go about getting some serious writing credibility, especially if you're new to the game.
Some of her recommendations: blog, submit stories to your local newspaper (then the state newspaper), write for online magazines (webzines), then to national magazines, become an expert on a subject and write about it.
There are lots of good ideas there. And it sure beats "I've always loved reading and am so excited to have finally written my first book" on your query letter.