Being on time, reading for the rotation, knowing your patients, being interested (without pretending you want to be a surgeon if you really don't) all go without saying. A good attitude is key - EVERY field has something to learn from that you can take to your future career. Try and figure out what that is. Do not roll your eyes when I describe the cases for the day because you have seen "lots of those"; do not be eating breakfast in the cafeteria when the patient is rolled into the room.
One of the things that impressed me about the student who just finished rotating with me was anticipation of events. When we would start discussing surgery with the patient, he would get the surgery booking sheet out and start completing it, the pre-op testing forms, etc. He would hang the films and even attempt to educate the patient on their problem. Most students don't IMHO. It was something little but it showed initiative, attention to detail and a willingness to be a team player - no student is above doing paperwork, moving the patient from the bed, putting on a Bovie pad, etc. because its all work that needs to be done and if I will do it, so should you. I've seen some students who act like because they are paying X amount of dollars for tuition they shouldn't be doing "tech" or "nurses" jobs.
That, and it was obvious he was reading, looking at the OR schedule ahead of time, the office schedule, etc. He didn't just stand around waiting for me to tell him what to do. He was practicing his suturing at home and it was evident as his skills got better. He was prepared, asked questions when he needed more information or to clarify his fund of knowledge. This from a student who has no intention of going into surgery.
In short, he was prepared and he made me more efficient (although I am always slower in the OR and office with a student/resident), so I could spend more time teaching.
Now not every attending will want you to be doing such things, but I think at least making the effort - get the forms out, know where they go, making sure that you know the schedule and read in advance for it (even if its just a few lines about the case), goes a long way.
Oh... and he brought me lunch on several occasions when he thought I wasn't eating enough.