When meetings Spanish people for the first time you usually shake hands. Men who know each other well greet one another with an embrace and a pat on the shoulder, while women kiss each other on the cheeks starting on the left. In formal situations you usually address people with Don or Doña plus their first name.
If you are invited to dinner at someone's home, you usually take a gift, such as chocolates, cakes, wine or flowers for the hostess. If the family has children, small gifts for them will be appreciated. You normally don't sit down until invited to do so and don't begin eating until the hostess starts. Most types of food, including fruit, are eaten with utensils rather than with your fingers.
If you're doing business in Spain, it pays to establish relationships as the Spanish prefer working with people they know and trust. They also prefer dealing with people in person rather than on the phone or by email, fax or letter. Don't be modest about your qualifications, experience and achievements as people are likely to take what you say at face value. Try to avoid arguments if possible as Spanish people tend to avoid admitting they're wrong in public.
When talking to people in Spain, you may find that they quite often interrupt you. They're not being rude, but just have a different way of doing conversations. Conversely, if you waiting for them to stop speaking before taking your turn in the conversation, you might find it difficult to get a word in edgeways, and they might think that you have little to say.