I think Tanyabeth really hit it on the head.
The server should acknowledge your presence, at least in passing if in the mioddle of doing something else. Drink orders should be taken promptly and the drinks served quickly.
The person should be familiar with the menu, willing to make suggestions if you ask. Most better restaurants require their servers to have at least sampled everything on the menu, so they can make recommendations based on their own experience.
Dishes from each course should be cleared promptly (but not if you seem to still be in the middle of eating). The different courses should be reasonably paced, which can be controlled by the server.
Non-alcoholic beverages (water, soft drinks, coffee, etc.) should be refilled promptly, without having to ask the server; maybe the server, toward the end of the meal might ask if you want additional refills.
The check should come around the time you are finishing dessert, and once you have left a credit card or other payment the charge slip or change should be brought back promptly. If you are paying with cash (or traveler's check) all your change should be returned unless you have given the server instructions otherwise.
This is my basic standard for a tip in the 15% to 20% range. I will expect the quality of service to be higher in a restaurant such as Bistro de Paris as compared to Dennys.
If the quality drops below my expectation I will lower the gratuity accordingly. If it drops such that the tip will be less than 10%, or it is such that I will want to leave more than 20% I will always have a discussion with the retaurant manager as to why.
And tip is always based on the pre-discount and pre-tax prices.