If they are polite, helpful, get everything right, and you are extremely pleased with their excpetional service, then you should feel free to tip up to 25% of the bill. If they have done a lousy job, and made your visit unpleasant as a result, then you should absolutely not tip at all. And your tipping should range between those two limits, in proportion to those two extremes of service.
Be sure to leave an orange card on the table that says merittippers.com on one side and doubleyourtips.org on the other side. Put this card out as soon as you sit at the table. Eventually all servers will know that this means you will tip based on their service and nothing else.
And always, no matter what the service, be polite and pleasant to the server. The orange card should always mean that we are being reasonable and fair.
I will send you ten cards, to get you started, for two bucks. Send two dollars and a self-addressed, stamped envelope to: