You should tip 15% for adequate service in restaurants and up to 20% if you feel you've been treated well. At higher-end restaurants, where more service personnel per table must divide the tip, increase these measures by a few percentage points. An especially helpful wine steward should be acknowledged with $2 or $3. It's not necessary to tip the maître d' unless you've been done a very special favor and you intend to visit again. Tip $1 per checked coat.
Taxi drivers, bartenders, and hairdressers expect about 15%. Bellhops and porters should get about $1 per bag; hotel maids about $1 to $2 per day of your stay; and valet-parking attendants $1 or $2 (but only after they bring your car to you, not when they park it). On package tours, conductors and drivers usually get about $2 to $3 per day from each group member. Concierges should get tips of $5 to $10 for special service.