To be honest, I don't think you can really tip too much; but generally speaking people tip between 15%-20%. If the service is terrible then you can give them a lower tip, but I usually like to give the server the benefit of the doubt and tip them well.

The norm for leaving a tip would range between 15 percent and 25 percent, but this could also depend on the type of service you receive whether good or bad. Some think that over 25 percent is much.

rate your service from 1 to 10 . start at 12% and go up to 22% really good service is worth more so go with 22%.. really bad service is worth less go with 12% . If you are a regular at this place then you might want go a little higher , this could affect the out come of your next visit !!! 15% is the norm

The average tip is 18%, while some people will tip between 15%-20%. Bad tips are usually around 10% or less, while good ones are 22% or more. If you are really impressed with the service, quality, etc., you can tip any amount you want. Some people have been known to tip 100% when they get excellent service.
There is really no such thing as tipping too much except when you are tipping for bad service. If you do not feel they deserve that tip, don't give it to them, or make it much less. One trick a friend of mine uses is to count up the number of mistakes/problems, and the number of things they excelled at. He usually starts with something like 15 items (like sugar packets or the like), and takes away one for each problem, and adds one for each thing they did well. At the end of the night, he tips the percentage based on the number of items on the table. If there are 10, he tips 10%, if there are 20, he tips 20%.

I used to work for tips so I always over tip! No tip is too much for good service!