Here are some tipping guidelines suggested by the National Restaurant Assn. in Washington, D.C.:

• Customers should tip at least 15 percent of the pre-tax bill. But when you receive good to excellent service, leave 20 percent.
• Remember that tipping is a monetary thank you for services rendered. But it’s still nice to give a verbal thank you as well.
• Tips make up a major portion of a server’s living wage. Many restaurants don’t even give them minimum wage.
• If the service is lousy, ask to speak with the manager to voice your concerns.
• Don’t exit without leaving a tip. Many times the restaurant is willing to correct the problem or offer you a discount. Restaurants want your business, and they don’t want to lose customers due to a rude or inefficient employee.
• Check your bill to see if the tip is already included. Some restaurants automatically calculate the tip for parties of six or more.

To learn more about tipping etiquette, check out the Web site of The Original Tipping Page, www.tipping.org.