In addition to drawing really, really well, my pal Tom Richmond is one of the wisest folks I know about the business of being a freelancer. His blog today has sound advice about a not-rare-enough situation for such people: You do a job for someone and then they either can't pay you or don't want to.
To all of Tom's sage counsel, I would append this: Beware of the client who is not really in business yet, at least on the project for which he or she seeks to engage you. Too often, they're trying to assemble the pieces of a deal and for example, they're hoping to use your work to impress someone to firm up the financing via which they hope to get the funds to pay you. When they insist they have the money, that's what they mean. I call these people Unfinanced Entrepreneurs and they are to be avoided, even though it may mean turning down what would be a great, lucrative assignment if it all goes according to their plans dreams.
Anyway, beware of them and also heed Tom's caveats and collection methods.