Here's more sociocultural information about Spain from an old GeoCities website I came across, with my comments within parentheses.

Conversation: Welcome topics of conversation in Spain

your home country (Not so good if you're American; perhaps your home state or city would be a good topic.)
travel
sports, especially soccer
politics (if you know what you're talking about) (I would avoid politics if possible. I would also avoid sex and religion.)

Topics to Avoid:
Bullfighting is a revered art form here. Consequently, it will be in your best interests to refrain from airing any criticisms about this practice. (Oh come on. Still, I'd avoid the subject simply because Spaniards are likely to take your bringing it up rather as an American takes being informed, say, that his fellow citizens are a bunch of fat ignorant gun nuts.)
Also avoid discussing religion and war. (Duh.)
Try not place too much of an emphasis on your professional experience and business success during conversation. In this culture, the quality of your character is the measure of respect. (Also don't say anything that might be interpreted as bragging. That's never good, but then you already know that being a sensible person. One Spanish stereotype of Americans is that they're braggarts. Prove them wrong by not being one.)
Avoid making personal inquiries, especially during first introductions. ("Are you married?" and "Do you live near here? and the like are just fine. "So how's your mistress?" might be considered a little forward.

Let's Make a Deal!: What you should know before negotiating in Spain

Personal contacts are essential for business success in Spain. Select your Spanish representatives with tremendous care: once you've made your selections, it can be extremely difficult to switch to other people. (I don't think that's true, but be careful because it's hard to fire people, by law. You need a good reason to do it and will likely have to pay the firee an indemnity.)
Bring business cards with one side printed in English and the other in Spanish. Present your card with the Spanish side facing the recipient. (Nice but hardly obligatory.)
You should be aware of the importance hierarchy and position play in Spanish business culture. For example, it would be frowned upon if you spent a great deal of time and attention on someone who is of lesser rank than you. It will be in your best interests to focus chiefly on those who would be considered your "equals." (I think they're overdoing this. Just be nice and courteous to everyone.)
Spanish business culture is extremely hierarchical, and only bosses, popularly known as el jefe or el padron, have the authority to make decisions. Generally, subordinates are required to follow orders, obey authority, and solve any problems before they surface. (Yeah, this is unfortunately true of many Spanish small businesses. Larger corporations are much more American-style.)
Be sure to take plenty of literature about your company to distribute. It will also be an asset to bring samples of your products and/or demonstrations of your service. (Duh.)
Most Spaniards will seek the support and approval of family, friends, and colleagues before acting on their own. There seems to be an underlying belief here that a person is not a part of society unless he or she is recognized as part of a group, neighbourhood, town or business organization. Consequently, there tends to be a resistance to the "outsider." Visitors to the country are expected to overcome their "outsider" status by ingratiating themselves into a group of some kind. (I'm not sure you have to join a group; I certainly haven't and I'm perfectly happy. It can't hurt as a means of integrating yourself within the society, though. Spaniards do seem to pay a great deal of attention to the approval and opinion of others.)
Rather than expecting Spaniards to conform to your way of doing things, you should make the effort to emulate their behaviour; this is one effective way of gaining the acceptance of your Spanish counterparts. When you make the effort to adapt to their ways, this demonstrates your respect for their culture, and also tells others that you are flexible. (Duh.)
Do not expect to discuss business at the start of any meeting. (True; there'll be a little small talk. Let the other guy decide when to start talking business.)
During a first meeting, Spaniards will want to become acquainted with you before proceeding with business, so be accommodating and answer any questions about your background and family life. (This is more true of small companies.)
Remain warm and personal during the negotiations, yet retain your dignity, courtesy, and diplomacy. The Spanish participants may initially seem restrained and indirect, but this is normal until your relationship has been established. (And isn't this true everywhere?)
Although Spaniards are receptive to new information and ideas, you may find that they don't change their minds easily. (Again, this is true of everyone. It can be tough to get a Spaniard off his high horse in a political discussion, but you can expect courteous behavior from Spaniards you deal with on business matters.)
Feelings are generally the source of truth in Spanish business culture. Consequently, it's important that you work at developing an excellent rapport with your Spanish counterparts. If they have a favourable impression of you, and believe that you can be trusted, the likelihood of your success increases. (Yeah, this really is true in Spanish culture in general. If they like you you can get away with anything, and if they don't like you you're screwed.)
Spaniards rarely use objective facts or empirical evidence to prove a point. (Unfortunately true. Spaniards are not great on logic and reason.)
Faith in the ideologies of the Church or nationalism can also be important influences in decision-making. (Religion, I doubt it. Most people aren't so unprofessional to let nationalism get in the way of making money.)
Spaniards generally expect the people with whom they negotiate to have the authority to make the final decision. (True; you're likely negotiate with someone of a higher rank than you. Decisions are made higher up the scale in Spain than America.)
Even if your Spanish counterparts seem friendly and encouraging, they may not be forthcoming with information they consider valuable. (True. Everyone wants to maintain his little empire.)
If you are interrupted while talking, do not interpret this behaviour as an insult or a cause for concern. More often than not, the Spanish participants' interruptions indicate genuine, animated interest in the discussion. (True.)
Honour and personal pride mean everything in this culture, and must not be insulted. (Oh, come on. Nobody anywhere likes being insulted. Don't insult people is a pretty good rule to live by.)
The Spanish give advice to one another and to visitors freely, but you shouldn't take offense at this. (And you will get sick of it pretty damn quick. Especially Spanish old ladies don't have enough with managing their own lives; they've got to manage yours, too, as well as everyone else's.)
As in many Asian countries, you must do everything you can to prevent yourself and others from "losing face", that is, losing control of emotions or suffering criticism/embarrassment of any kind in the presence of others. (True. They don't like that one bit.)
Ensure that your presentation is comprehensible. During a meeting or presentation, you will have to take the initiative to discern if your audience understands you. Since "losing face" is viewed so negatively in this culture, people will not admit in front of others that they are having difficulties. (Right. They won't tell you they don't understand. You need to speak slowly and clearly, and repeat important points.)
Spaniards often feel a need to be careful about what they say and how they say it. In any but the most private moments with trusted family and friends, speaking "the truth"--if it is unpleasant--is approached with extreme care. (They can be overly diplomatic at times.)
Particularly when dealing with outsiders, Spaniards will often insist that everything is in perfect order, even when this is not the case. This is a "face-saving" measure to appear competent and in control. You may have to pay close attention during conversations with your Spanish contacts, to discern the sincerity of what is being said. (True. Everything's always just fine, no pasa nada, sin novedad.)
Because of the reluctance among Spaniards to reveal bad news, it may be important to have a network of independent, disinterested contacts that can verify or interpret what you are being told in your business dealings. Spaniards who have worked or been educated in the West may be valuable contacts for this purpose, since they are more likely to be sympathetic to your desire to know the truth. (It is better if you have a trusted source to consult with, but that's true everywhere. Another thing is that several of these Spanish cultural attitudes mentioned here are known to all Spaniards who read business books, and they do their best to avoid behaving in these "old-fashioned" ways. A young business school grad is going to behave in ways more or less like yours. It's the old guy who runs his own small business who's likely to be quirky.)
It's important that you stay involved with your Spanish counterparts, helping to implement what has been agreed to. This must be done with sensitivity toward the pride that Spaniards feel in being able to handle things independently. So, never be intrusive, but always be available; express an interest in learning about their ways, while providing them with the resources and information they need to reach their objectives. (Tell 'em what to do or nothing will get done, but don't be too obvious about it.)
Although relatively few Spanish women are in management positions, businesswomen traveling to Spain will be treated with respect. Dressing and behaving in a professional manner remains essential at all times. (True. For you. Some Spanish women in business sure look trashy. Don't do that yourself.)
It is important for female business travelers to understand that machismo is very important to Spanish men, and they often feel the need to be in control of all situations. (Much more true of old guys than younger guys, though you'll be surprised at how retrograde many Spanish men are.
Spanish men are usually willing to accept a lunch or dinner invitation from a businesswoman. As in most countries, the person that extends the invitation pays the bill. (True.)
Decision-making can be slow and tedious: various levels of hierarchy will be consulted and all aspects of your proposal will be analyzed in painstaking detail. (True. Decisions will be kicked upstairs.)
Power is intrinsic to Spanish business culture; only the highest individual in authority makes the final decision. Therefore, understand that you will often be dealing with intermediaries. Maintaining an agreeable relationship with these intermediaries, however, is still crucial to your success. (Duh.)
In Spain, the use of the familiar tú and the formal Usted methods of address are different from their usage in Latin America. For example, Spaniards always speak to domestic servants in the formal Usted manner. They feel this confers dignity and shows respect for the servant as a person. Also, the informal tú is more likely to be used by colleagues in a Spanish office than in a Latin American office. Sometimes employees even speak to their bosses using the informal tú. (General rule: use tú with equals, usted with people in authority or older people. Use usted if there's an exchange between you and a service person, a taxi driver or bartender.)