Let me save you $10. Here is the advice contained in this booklet.
Send your work to people.
Make some t-shirts and posters. Sell them to supplement your income.
Network. Network by going to formal events, but also go to parties and randomly meet people because this is where your best contacts come from. (Sadly I find that to be completely true.)
Learn new stuff. New stuff you can learn: Animation/Motion Graphics, Programming, 3D. You should/could learn this things.
Manage your time well.
Work on your portfolio.
Work out your pricing ahead of time.
Know what you're doing before you do it.
The topics I've presented here are only slightly less deeply presented in The Designer's Guide To Going Freelance.