Here’s what I’ve heard:
General rule: Breakfast*: 10%. Lunch: 15% Dinner: 20%
*”I’m going to work” breakfast. Not “I’m finishing a pub crawl” breakfast.
Why: Breakfast sees a lot of turnover in guests during the period. Lunch less so. Dinner least.
The rule is 15% regardless if it's breakfast, lunch or dinner. If service was less than adequate 10%. If service was outstanding 20%. If service was awful, leave a couple of pennies, but only if the service was just awful. The wait staff may get mad, but at least they will know that you were unhappy and not just cheap.
Anytime you have someone wait on you, they deserve to receive a tip.