Forget about checking bank references if you're going to do work for a start-up. Ask to see the business plan, says Bill Drenttel, head of Drenttel Doyle Partners, a Manhattan design agency.

While it's always nice to get paid, if your client goes out of business before getting its product to market, you have nothing tangible to show for your effort, says Drenttel. That makes it harder to solicit new clients, who are going to ask to see examples of your work.

"We now always ask to see a business plan before we agree to do anything for a start-up," says Drenttel. "And if I don't understand the idea, I pass the plan along to a friend who does. I've learned that what I think is a neat concept is no guarantee of anything." So far, Drenttel says no one has balked at his request.