Do's:
Greet everyone in the room with a handshake or kiss check (males only handshake other males, females kiss chick everyone)
Say "buen provecho" at the end of the meal
Offer to pay at a restaurant or accept for someone else to pay. It's rare to split bills in social situations.
Have a lot of patience, things happen very slowly and many times don't work at all
Don't:
Deny receiving a gift, it's offensive.
Expect people to turn up on time for anything.
Have faith in directions on the street, people prefer to give false directions than admit they don't know
Be offended if someone doesn't come to a party when they say they will, people prefer to say yes and not come than say no
I'm sure there's many more that I can't think of the top of my head.