These are in no particular order and just what come out of the top of my head:
1) Just... Senior year is a bad time to study abroad. I'm kinda dying here between stuff I've got to do in the IS, senioritis, twice as many weeks of school as normal in a row.... Yeah, just study abroad in junior year if you can.
2) On the other hand, studying abroad when you've had as much language study as possible at home helps you to really get the most out of your experience. So, I really do advise waiting until you've taken as many language classes at home as possible/reasonable.
3) Working in groups with local students can be interesting, to say the least. It wasn't bad, I guess, but since they all knew each other and I'm a foreigner and a stranger they kinda disregarded that I might be able to speak Spanish and I might have interesting things to add. So that was interesting.... But I'm sure that not everyone has that experience, and there are other students who I suspect would be a lot nicer.
4) A lot of people in shops or whatever like to try to practice their English... either that or they just think I can't speak Spanish when I hesitate for a second. Or they're racist. I don't even know, but I try to give them the benefit of the doubt and assume that they just want to practice their English.
5) Getting out there and doing something with the community is a great idea. Especially if nobody speaks English in the group. It gets you involved in the culture in a whole new way. My thing was choir, but I also strongly considered volunteering, and I'm sure there are a million things out there that you could find to do. Just do it, it's something you'll never regret.
6) And don't bite off more than you can chew. A word to people from schools that run on quarters picking classes with semester credits: It's not just when you transfer them back home that 3 semester credits equal 4.5 quarter credits. It's also in the day to day workload.
7) Tutoring was nice, while I did it. Just be okay with asking the parents questions about their kid and asking for help elsewhere too. But if you like working with kids and teaching, it should be a good experience.
8) I'll just repeat what I was told, by one of my favorite professors, in my freshman year of college: You're doing a lot of studying, yes, but find something that's just good for your soul. Whether it's music or escaping to the hills or travelling (if you can afford it) or reading books or anything at all. Just find something that helps you relax and be you and not worry about life as much. (A lot of people like being in the city, but I kinda dislike flat cities, so I've taken plenty of solace in books and choir.)
9) Be open to making friends. So be willing to spend time with people when they invite you to do stuff with them. I'm rather reserved and used to living on a college campus where it's easy to just run into people, so I haven't done that great at that, but just be willing to put some effort into talking to people and making a connection with them.
10) People in this country can be incredibly nice. Like, they actually pay attention if you look like you're having a hard time, or at least some of them do. And it's driven me insane, because I hate crying uncontrollably and I can usually hold it in until I'm alone if people leave me alone. But it's also great, and if you see that someone looks like they might care and you need to talk, you're probably safe to do so. Just don't worry about it. (Also, I've found that the other american students are really nice too when I need a listening ear. People really do care about you who aren't thousands of miles away. Trust me.)