Depending on the region or the religion, the ways of greeting others can vary quite a bit. Here's a brief summary to help you avoid making a faux pas.

Touchy-feely

In Europe, people are pretty demonstrative. Kissing on the cheeks is the way the French and the Belgians say hello, while warm embraces and big hugs are the custom in Spain and Italy.

At a distance

In Asia, restraint is the rule. The customary salutation in Japan is bowing, or ojigi. The depth of the bow and how long it lasts vary according to the social occasion, the age of the person to whom you are bowing, and your own ranking.

In Thailand, the wai is the proper way to greet others. This is done by pressing your palms together; as if to pray, at face level. It is polite to respond to a wai with a wai, unless the other person is a child or a person performing a service for you, such as a salesperson or a waiter.