I started straight from nursing school
to the ICU-it is a huge learning curve but one that I loved and wouldn't trade for the world. I would start getting to know the emergency medications and patho of the major stuff you are going to be seeing (heart, lungs, GI, etc) so that those things can be a little bit more ingrained.
Having said that, it is really a learn on the job thing-take the basics you know (and they are very much basic) and watch. Learn, reread about the patho and drugs that you come into contact with every day, and know that most of what you learn is going to be on the job with your feet running.
I am assuming that you will have at least 6 months mentorship-if not, I would think hard about the job. That 6 months was spent doing the things I said above, as well as hammering my poor mentor on all kinds of questions and skills.
Like I said, I wouldn't have changed it for the world. It is definitely demanding and you need to be able to study after your shift to keep up for the next day but it is good if you are willing to put in the extra time and energy..