Go over how to interview if you're unsure so you don't walk out of a patient's room and say to your resident, "no i didn't ask that, or that either, or this, or that." It's still going to happen no matter what, but it's good to review. And know how to do a physical. For example, don't just know where to listen to different heart sounds, but know how to do a full CV exam including pulses, PMI, etc. Pocket Bates is awesome and I'm amazed that more students don't carry it because reviewing it for 30 seconds before going into a room saved me plenty of times.
It's a good idea to review EKGs. They can really tell you a lot of information and if you're the one student on your rotation that can interpret them then you look good immediately.
Know the approach to reading a chest xray, but until you've seen a ton of them you won't be able to tell what's normal and what's not. Do you have Step Up to Medicine? There is a good guide on how to evaluate them before you start.
Do you know how to write a note at all? Some schools teach it and some don't, but learn the basics of an H&P note and a SOAP note. Depending on where you are, your hospital might have a basic form you fill-in-the-blanks, or it might just be blank sheets of paper. This is another time pocket-sized Bates was helpful. Learn how to do a SOAP note (what belongs in subjective, what belongs in objective, etc). IM docs and residents write a lot, and they'll expect you to do the same.
Truthfully, there's not really a "high yield" list of things to go over before you start an IM rotation because it's such an enormous field. If you're comfortable interviewing patients, doing physicals, and can write a decent SOAP note, you should be in good shape for your first few weeks.
