While the ideal "host family" situation that la maestra describes really would be great, I think the term "host family" often takes on a really different meaning a lot of the time. Ive studied abroad twice, and both times lived with, what was always called a "host family". However, they were paid to keep me.
The first time, in Bilbao, even though they were being paid, the family was AMAZING. I was the first exchange student they had ever had, and I really felt like a member of the family. I still keep in close contact with them and have visited multiple times (not paying, and they insist on paying for everything, its really sweet).
That said, and I dont mean to make anybody mad by saying this, good situations can always be found.... I think the experience I had in Bilbao was the exception, not the rule. They werent in it for the money, and that was clear (to this day Im the only student theyv ever hosted). I found that out really quick during my second study abroad experience with a host family, a semester in Granada. This 2nd host family situation was awful. They clearly were in it only for the money, and could have cared less about who I was, or getting to know me at all. It was pretty much: here is your room, meals are at this time, have a nice semester. Very unfriendly, and not a good situation. They had hosted students for almost 10 years, it was pretty much a job, and they made that pretty clear from day one. Luckily, I hade already been living in Spain for a while, and really didnt care, since I was hardly ever at home, and was still in close contact with my Bilbao family.
I don't mean to scare you away from a host family in any way. With a good family, it can be a wonderful experience. But really check it out before making that decision. If you could swing it, the ideal situation would be living in an apartment with spanish roommates your own age.
Kelly