I used to be an exchange student in Valencia, and I’ve done a fair amount of research on teaching English abroad (haven’t actually taken the plunge yet, though), so I can probably offer some tips about both professional and cultural issues:
First of all, some resources about teaching EFL: I suggest you check out the website www.eslcafe.com and also pick up a copy of a book called Teaching English Abroad, by Susan Griffith. This book is an excellent introduction to life abroad in general, teacher training, and working conditions and laws in various countries. Be aware that it’s mainly written for a British audience, and some things are likely to be different for an American. (Pay special attention to the regulations involving EU nationality – you’ll find it hard, if not impossible to work legally, although work under the table seems to be readily available in Spain, so I wouldn’t regard this as an absolute obstacle.)
Also, realize that there’s a lot more to teaching English than being a native speaker – at the very least, you need a solid understanding of how the language works, good communication skills, and the ability to empathize with your students and identify areas where a non-native speaker is likely to encounter problems. Thinking about things your own foreign language teachers have done, or failed to do, is a good way to begin gaining insight into these issues, although personal experience can only go so far – remember that you’ll probably be dealing with a variety of learning styles and some different cultural expectations about what should go on in the classroom. Talk to experienced teachers, and check out a few English textbooks and perhaps even some professional writing about foreign language pedagogy; if you know what generally works in the classroom, you’ll save yourself and your students a LOT of grief.
Sorry, I don’t mean to lecture, it’s just that if you do decide to teach, you owe it to your students to take the job seriously.
About life in Spain, in general: If you speak Spanish, it’s easy to meet people and make friends (well, maybe a bit easier if you’re a blonde female). One popular topic of conversation is politics, and people are not shy about criticizing foreign governments; many Americans find this difficult to take. Expect to get into a lot of arguments about gun control and the death penalty, even if you disagree with American policy on these issues (most Spaniards have a very media-distorted view of what actually goes on in the US, so they make it easy to argue. You, by the way, will sound equally clueless if you try to enter into a discussion about the ETA; I’ve done it and I don’t recommend it.) Anyway, keep an open mind and don’t be too sensitive to criticism of the US – it’s not (usually) personal.
As for where to go – it’s an extremely regional country; you can travel for a few hours and be in a place with a completely different feel to it. I’d suggest traveling around and getting a sense for where you feel comfortable before you try to settle anywhere. If you want the classic Mediterranean climate, with orange trees and great beach weather, go south; the north is cool, rainy and green. In Madrid and Barcelona you’ll find a lot of English speakers; in most other places you won’t (this is probably a good thing, given that you want to teach English and learn Spanish, but it means life can get lonely at times). Wherever you go, read up on local and regional festivals and try to attend as many as you can – it’s quite an experience.
The food and wine are cheap and really, really good; the beer is lousy, but you can get Guinness everywhere; the coffee is without question the best on earth.
Well, I’ve stayed at work half an hour longer than I meant to, and this post is just about the length of a short novel, so I’ll stop. Have fun – it’s a great country.