In America it is customary to tip when you eat out at a restaurant, between 10-20% is normal. Following is some advice:
RESTAURANT TIPPING ETIQUETTE
Although excellent service calls for 20 percent of the total bill, most 
U.S. restaurants accept 15 percent as the standard tip. In restaurants 
where you sit at the bar or the waiter is a small part of the meal 
(cafes or pubs), 10 percent is also acceptable. The bar tenders, 
themselves, generally receive between 15 and 20% when you sit at the 
bar. If the food or service is unsatisfactory, speak to the manager - 
don't walk out without tipping. And pay attention to lunch and dinner 
bills in Europe and Asia, as some restaurants tack on an additional 15 
percent (usually listed on the menu or check as a "service charge") and 
do not expect tips.
At fancy restaurants, tip the maitre d' between $5 and $10 if he gets
 you a table - more when the restaurant is full and you have no 
reservations. Tip $1 when you check your coat, and another $.50 to $1 
for restroom attendants. For personal service from the wine steward, opt
 for 10 percent of the wine bill.
This tipping etiquette will hopefully give you a general idea of the 
standard tipping rate for different stops along your journey. You are 
always welcome to tip more when the service is excellent, and when you 
do, you are sure to see the red carpet treatment all the way. 
TIPPING AT AIRPORTS AND TRAIN STATIONS
Upon arriving at or leaving from the airport or train station, tip the 
standard porter rate of $1 per bag; more if your luggage is very heavy. 
Typically, a $1 tip for hailing a taxi is appropriate for doormen. 
However, you may want to tip more for special services, such as carrying
 your bags.
HOTEL TIPPING ETIQUETTE
When you arrive at your hotel after a long flight, first things first: 
Tip the taxi or limo driver. Ten to 15 percent of your total fare is 
usually expected. If you drive your own car, give the valet parking 
attendant $1 to $2. If you take a shuttle van or bus, tip the driver $2 
per person.
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The bellman, who will be more than happy to assist you with your bags 
and the door, should receive $1 to $2 per bag. Tip when he shows you to 
your room and again if he assists you upon checkout. Tip more if he 
provides any additional service. The concierge, who can get you anything
 from dinner reservations to hard-to-come-by theatre tickets, deserves 
$5 to $10 for such feats. You may tip at the time of service or at the 
end of the trip. To ensure good service throughout your stay, add a $20 
tip to the bill.
Add 15 percent of the bill to a room service charge, unless a 
gratuity is already added, then add no additional tip or simply $1. If 
you requested something delivered to your room such as a hairdryer or 
iron, tip $1 per item received. Typically, the maid deserves a $2 tip 
each day, as well.
TOUR TIPPING ETIQUETTE
If you're taking a tour and a tip is not automatically included, tip a 
local guide $1 per person for a half-day tour, $2 for full-day tour. Tip
 a private guide more.
If you are on a multi-day tour with a tour manager - someone who 
travels with the group for several days and is essentially in charge - 
tour operators suggest anywhere from $3-8 per person per day. Don't 
forget the bus driver either - $2 per person per day.
CRUISE TIPPING ETIQUETTE
When on a cruise, tip according to your comfort level and only on the 
last evening of your cruise. As a general rule, dining room waiters 
receive $3.50 per person/per day whereas the dining room assistant 
waiter should receive $2.00 per person/per day, the dining room maitre'd
 $3.50 per person/per day and the dining room manager $1.50 per 
person/per day. 
The room steward, for all his efforts, receives $3.50 per person/per 
day. Other personnel, such as bar waiters, bellboys and deck stewards 
may be tipped as service is rendered.