Work hard. Come in early, stay late, offer to do extra work wherever possible, ask to take on more patients (but only to the extent that you're able to handle it), know EVERYTHING possible about your patients, spend time with your patients, ask questions. And definitely be friendly.
Also, no need to be coy about the fact that you're looking to impress and/or match there. On day 1, tell your supervising resident what your goals are, and ask him/her what the best way it is to accomplish that.
As has been said already, nobody expects you to know a lot of stuff. Of course it helps if you're more knowledgeable, but that's not what's expected of a student... after all, you're a student, and you're there to learn. So don't be afraid to ask questions due to a concern that it'll make you look less knowledgeable. You'll learn so much in residency that it'll pale in comparison to what you knew as a student... so the student with a lot of knowledge will eventually balance out with the student with a bit less knowledge after residency, and that's why residency programs aren't necessarily looking for a person with the most knowledge, as long as you're interested in learning and you're hard-working, since that shows that you'll develop quickly as a resident.