"50 percent to 60 percent of your customer base will be one-time buyers or visitors. Accept it. You'll waste a ton of money trying to change it, and it's not going to change. One-time buyers who bought multiple items on the first purchase are a possible exception. Try them first. Then try one-time buyers with the highest order value. If these don't bite, none of the one-time buyers will."
Read the rest of Jim's ideas on customer-focused marketing promotions