Dane at the Business Opportunities Weblog shares several great consulting tips he found (via Pablo Corral) on a Google message board.  Dan has the entire list, but here are my favorites:

• I always take the approach that no problem or question is stupid.  And I make sure the client knows this.
• I always give a verbal summary of everything I've done in as plain of English as I can when I finish a job.
• Ialways leave two more business cards with a client when I finish, andexplain that I'd appreciate any referrals they could give me.
• I always call to follow up the day after a major job.
• I do NOT charge for phone support.
• I do NOT charge for travel time.
• I send thank-you cards after payment is received.
• IfI'm not doing client work on a given day, I dedicate that day tomarketing efforts (letters, press releases, networking, etc.)

Print out this list and put it in the front of every client file you open and look at it several times thoughout the engagement.  I especially love the thank-you card idea.