With regards to the electives themselves, it should be clear that you need to approach them with the idea that the elective is part of your interview. If you know your material and function well they will give you serious consideration during the interview and match process, if not, well then you have just shot yourself in the foot.
I must say that personally, there were places that I didn't like at all the moment that I began my elective. The people weren't nice, things were a mess, and I just didn't take a liking to the place. Of course, that affected the amount of extra effort I put in on that specific elective, but I never mentioned a word or showed my discomfort to anyone. Furthermore, even in such unpleasant electives you never know when a different, more amicable, player will enter the game (for example when you switch surgery teams) and change your perception. Finally, many times people work at more then one hospital and word gets around - be careful.
Last but not least, do not forget that you are representing your school. If you leave a bad impression they will simply choose to exclude people from your school from future electives, which will affect the classes below you. Even if you're sure you won't rank the specific hospital please do your best, be respectful, and leave the place with a good impression of IMG's/FMG's.
Letters of Recommendation
As you'll hear many times, the US programs regard US letters of recommendation as superior to letters from other countries. Whether you like it or not this means you need to get excellent/fabulous/amazing letters of recommendation during your first two electives. Do not mistake the fact that you are coming from an underdog position as a foreign graduate and that you need to wow them and not the other way around.
That means coming in on weekends, holidays, staying late and doing more then they expect. Common sense that leads to excellent recommendations.
Additional Tips for Success
To maximize your success you need to also make sure you live in relative proximity to the hospital where you're doing your elective. I did one elective in the Bronx while living in my apartment in Chelsea. It took about two hours to get to the hospital every morning and that definitely affected my success (it did save me a move though..). If you can, try to avoid my mistake.
Application & Interviews