There are two ways to improve your service, and yourself: maximize your strengths and minimize your weaknesses.
If they're going to remember the problem, make sure they remember it fondly.
If your customers are demanding, be thankful.
Occasionally problems will occur. When it happens to your customers, fix the problem fast. Make it your speed and generosity that gets remembered, not the problem.
Don't wait. Tomorrow may be too late to do the things you can today.
If your customers have to ask you for it, you haven't been thinking far enough ahead.