I love to tip well but I base it on the level of service. Below adequate - nothing, just adequate - 15 to 20%, good service 20 to 30%, excellent service 35 to 50%. I have on rare occasion left a 65% tip. I like to use the philosophy of "take care of those who take care of you."
Servers depend on their tips to help them survive. Their salary is different than other employees. In an average restaurant never leave less than 15% for lunch & never less than 20% for dinner. If it's a "fancy restaurant" never leave less than 20%-25% for lunch, dinner 25% & up.