If you're getting ready to go abroad, your main concerns probably include finding your passport, buying enough sunscreen, and wether to pack your own toilet paper. Tipping etiquette in your destination of choice probably hasn't even crossed your mind.

Friendliness and courtesy are universal, yes. But the tipping norms that apply when it comes to taxi drivers, restaurants and hotel staff can vary just like any other social custom. Except, in this case, it's your money.

"You feel so vulnerable when you go to a country and you don't know the local tip customs," said Don George, global travel editor at Lonely Planet Publications. "You wonder if you're giving people money they don't expect, or so little that you've offended them."

Don't worry. Learning to tip abroad isn't really that hard. Things do vary from place to place, but you can stay on top of it. There are a few guidelines below that are flexible enough for many international situations, and more individualized guidelines for your destination can be found in good travel guidebooks and Web sites.

Step one: Go to the bank. Exchange your money for the foreign currency you need, and get small denominations -- tipping means you need change. And don't wait until you get there. Tipping issues will pop up as soon as you step off the plane.

"When you're dealing in the currency of the country you're in, make sure you're not over- or under-tipping," said Peggy Post, etiquette consultant for Good Housekeeping and Parenting magazines. "It might sound like what you're giving is a lot. The best thing is to do a little advance homework and find out."

This can be particularly daunting in countries with highly inflated currencies, said Douglas Stallings, an editor and travel expert at Fodor's. Two thousand Bolivares sounds like a lot of money. In Caracas, Venezuela, it's about $2.

After you know how much your new money is worth, get your hands on an up-to-date guidebook. It should tell you what amounts are customary in specific situations. (In a few destinations, like Iceland, New Zealand or Fiji, you might be surprised to know that people don't tip at all, Stallings said.)

At many international destinations, it's normal to find a 10 to 12 percent service charge added to a restaurant bill. "In most of Europe, there's always a service charge added to a restaurant meal, but it's expected that you'll add a little bit more," said Stallings. This can also be the case in the Caribbean or in more Westernized parts of Asia, like Hong Kong. You will see the service charge clearly marked on your bill.

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But you don't have to add another 15 or 20 percent to the total ? just add enough so that the total gratuity, including the service charge, is about 15 to 20 percent.

Still wavering on whether you should leave 15 percent or 20 percent? Keep a few things in mind. You should always tip for quality of service -- that's universal. "If someone does something extra for you, of course you want to be more generous. If you get bad service, you don't tip a lot," said Sue Fox, author of "Etiquette for Dummies".

Next, keep in mind where you are. If you're in a big city, in a well-traveled destination, and in a posh establishment, your tip should be on the higher end. In big cities, or places like Italy or France, tipping will be more common and bigger tips will be expected, Stallings said.

At the hotel, tip according to quality of service and the location, as you would in a restaurant. Anyone who does something extra for you should receive a tip.

There are a few unique situations: If you go to a resort destination in the Caribbean, for example, they may add service charges to your bill for restaurant meals and for the hotel stay. At some resort chains, like Sandals in Jamaica, no tipping is allowed.

"Sometimes, a substantial service charge is added on ? say, 11 to 17 percent ? but it usually includes taxes. In Aruba, for example, you'll see an 11 percent service charge, taxes included. Even so, you should still tip if it is allowed. If the service charge is about 10 to 12 percent, I'd add about 5 percent more," Stallings said.

It is customary to tip the maitre 'd, the hotel maid, and anyone who carries your bags. "If you want really good service, expect to tip," said Fox. "If you tip the maitre 'd, for example, you will be more likely to have a taxi when you need it, theatre tickets when you want them, and so on."

Remember to keep in mind who probably gets paid out of that service charge, and who might not. People like the hotel maid, for example, or a hotel tour guide, generally get paid less -- and depend more heavily on tips as part of their income.

"Of all the people in the hotel, the maid is least likely to see any part of that service charge and they make the least of anyone on the staff. Those are the people you should try to recognize in a direct way. Leave the money on top of your pillow, and leave it every night -- you may not have the same person making up your room every day. They will appreciate that, and you will get better service," Stallings said.

Others who expect tips include skycaps who carry your bags and taxi drivers (except, of course, in countries where no tipping occurs at all). Those who carry your bags for you should always be tipped, Post said. "The rule of thumb here is $2 a bag, but don't just hand out the equivalent amount abroad. Find out what is normal and customary," she said.

As for taxi tips, a little small change is fine in destinations where tipping is not so pervasive, Stallings said. In a more tip-friendly place like Paris, a cab driver could get up to 10 percent.

"In Japan, I never tip a taxi driver or someone who carries my bags, because tipping is culturally inappropriate. In England, I think taxi drivers expect a 10 percent tip and some sort of equivalent for carrying bags," George said. "I think the 10 percent rule is about right for cabs in tip-oriented destinations."

Whatever the situation, remember that tipping is really the way to say thank you for a service, Post said. "Say thank you -- don't just throw over the money," she said. "Be thoughtful about it. Be sure you're extending your gratitude. That's key for being a good ambassador, after all."