Kissing a woman on the cheek is the norrm.
Men sometimes kiss other men on the cheek, but this is more often reserved for friends.
Eye contact is a good thing in most settings. The exception is for females in night clubs where eye contact can be misinterpreted.
I absolutely agree that saying "buen dia" when entering a taxi is an excellent idea. I think honoring this custom will help reduce the probability of the taxi driver trying to scam you....not only is it polite, it shows you understand local customs and are not just some rube from the States.
Wagging your index finger and making a clicking sound with your tongue to a street vendor who follows you and will not desist...is a firm way of saying NO, I am not interested in your product or in giving you " monedas."
Veritas makes some good points about topics to avoid...but if someone initiates conversations with you about politics or soccer....by all means join in....I have had some spirited and enjoyable conversations on these topics with Taxi drivers and others....
Edited: 29 January 2010, 4:32