20% on meals if you enjoyed it. 15% is standard. In many places that is (or was) "double the tax," but now tax on meals is 9-10% or higher. Then there's stuff like cabs, doormen, bartenders. That can truly get a bit confusing even for a Yank like myself.
See I look at it completely differently. Especially with food, but really with pretty much everything.
I am tipping the service provided, not the food. The food is expected to be good. The wait staff should be penalized if the food isn't right but their level of service is excellent. But yeah...20% is kinda a standard. Valets get a couple of bucks. Same with doormen. Bartender will get an extra buck per drink if they are decent. Cabs I'll usually do about 10%.