What is the best way to break into copywriting or freelance copywriting?

I have done some reasearch on copywriting. It seems to be a very interesting and profitable career field. However, I have no clue on how anyone would go about starting a career in this field. I am particularly interested in freelance copywriting. I was wondering if anyone out here had any good advice or tips on how to start out in this business. I would like to start on a part time basis doing freelance work and hopefully take it from there.