A general rule is that tipping 20% is usually the safest amount, indicating that you are a competent, generous person, and that you are satisfied with your service. If you had a great meal with wonderful service provided, 25% communicates your gratitude. A 15% tip indicates things were adequate, and less means that they weren't good.
Remember when calculating the tip, that there are things wait staff in restaurants have no control over. They may be out of your favorite dish, or only have a tiny table for your party. Opinions about those types of issues go to the manager.