I would also recommend reading something specific for the rotation that you are scheduled to begin. I.e. first aid for the wards is a good choice. I think that it would help to talk to fourth years who have done the rotation that you are set to begin. Before third year my understanding of paperwork, complexities of medicine, or job of dealing with patients did not change much after third year, (I already had alot volunteer/work in hospitals).
But what did change which sort of crushed my optimism was an unawareness of the lack of inclusion of the medical student on the care team, and the presence of attendings who become more of a problem, and occassionally a source of great distress. In many ways, becoming a medical student is a step-backwards, i.e. you will be more poorly treated by some residents and interns than you thought possible, and if you are unlucky enough, you may become a taret of abuse by attendings. This is only a WORSE case scenario, so don't let me freak you out, but I think that it is essential to have a plan B if the "working" situation becomes unbearable on he wards. I.e. have a good advisor with whom you can talk to about a volatile situation, if it something that is really distressing you. NEVER talk to anyone in your Dean's office, they are there to support the faculty regardless of their behavior, and are not helpful when it comes to a difficult situation.
When you are in a couple rotations your conversations with family or SO will change from I am stressed out about the biochem final, to "My chief resident really hates me and today . . . I can't wait for this rotation to end so I can get away from this person." It is sad, but patient care, and education takes a back-seat to the daily meaningless hassels that are *purposely* thrown in the path of medical students by "old school" attendings who like to stress students to the breaking point and beyond . . . There is nothing that gives a resident/attending greater pleasure than berrating a medical student. What they don't tell you at the open house for medical school two years ago is how you become more an indentured servant with no rights during third year.