I agree with Kenny. Take time to have fun before intern year starts. But also be prepared.
For me the most challenging part of intern year is the dreaded cross-cover calls...when I have to cross-cover patients I don’t know overnight. My advice would to be sure you can be decisive and quick in working up and treating the common cross-cover patient complaints:
fever
hypotension
hypertension
tachycardia
shortness of breath / increasing O2 requirements
chest pain
post-op pain
nausea / vomiting
altered mental status
No one will ever fault you for ordering a diagnostic test. Although it may not be the most cost-effective for medical care, when you are cross-covering and don’t know the patient you will not be faulted for ordering things like chest x-rays, blood gases, CBCs, electrolytes, troponins, lower-extremity ultrasound, urinalysis, etc., before calling the senior resident. If you’re worried about a patient, load the boat and let your upper-levels know that you’re concerned but be decisive and have a plan, even if it’s just a diagnostic plan. However, don’t call your seniors if you don’t have all the info; go see the patient, know what procedure they had done and when, know their current vital signs and how they’ve changed compared to normal, know their latest lab results & imaging or at least have them ordered.
Nurses can be great resources as they have likely seen all this before but don’t let them bully you into something you’re not comfortable with. Think things through.
It seems to me the interns that have the most difficult time and seem the most stressed are those that lack confidence. You’re a doctor so act like one. Showing confidence to the nurses and patients will relieve everyone’s anxiety. When you’re right you’ll feel like a stud. When you’re wrong at least you made a decision.
The moral of the story is that as an intern you should be able to keep any luke-warm piece of humanity alive until morning when the rest of the team comes in.
The other things Kenny mentions are also important. Know how to close skin...it’s Ok to be slow at first. Know how to write post-op orders / admit orders without missing the often overlooked things (pain, nausea, sleep, constipation). Learn how to dictate a good discharge summary (key word here is summary) and operative note (although the latter is often a more upper level duty; if you can do it as an intern your seniors will appreciate it). Know your patients before you operate (even if you are just called in to close skin)...it will help you a lot when you’re taking care of them on the floor. Learn to be efficient at pre-rounding. Know how and when to replace electrolytes.

There is a good little book called the The Surgical Intern Pocket Guide that is pretty helpful for all these things; has sample dictations and such.
I’ve had a great intern year thus far (and just 4-1/2 months to go). Of course I’m crapping my pants in regards to my R-2 year, but, Kenny will be my chief and I know he won’t mind when I call him at any hour of the day or night blubbering like a school girl because I don’t know what to do with the latest shunt malfunction that comes into the ER.