Most of this has already been said, but if enough of us are saying the same things, then they probably hold true across various programs and situations.
I would reiterate Kim's advice re. double-checking to make sure your orders (AKA "suggestions") have actually been carried out, patients are peeing, etc. I call them anti-sabotage rounds. Plus it gives you a chance to fend off any 2am calls that could have been handled at 10pm had you only known about the problem. Since we don't pre-round at my program, it's very easy to get caught with your pants down on AM rounds if you haven't taken some serious CYA measures--I usually do a quick flyby on everyone before rounds anyway, just to CMA.
Exercise!
I'm at a very top-heavy program, which I pretty much knew going into it, but I came from a med school where the interns operated a ton. Adjusting to that has been pretty frustrating, so reminding myself why I chose to come here (amazing critical care experience, fantastic co-residents) has been critical to my sanity. That being said, again, I would reiterate the advice about choosing your program very, very carefully, asking lots of questions, knowing as much as possible about what you are getting into before you sign up, etc.
Exercise!
Be nice to nurses, but don't let them push you around--nip assault paging in the bud! Tactfully, of course. (I got paged 5 times in under 3 minutes by one nurse while I was in the CT scanner with a ventilated patient just because she wanted to give an extra 5mg oxycodone, which I had already written for incidentally, to a patient who was going home the next morning.) On the other hand, good nurses can save your @$$ and alert you to impending badness before the $h*# hits the fan.
Did I mention exercise? This is a total sanity saver, plus most interns seem to gain weight, which doesn't do much for sagging morale.
Ditto writing everything down--your memory will fail you at a critical juncture if you don't--and check things off as you complete the tasks.
Make sure you have a good working relationship, if not actual friendship with your co-interns. Inevitably, one of them will pull you out of a hole at some point, and you'll do the same for one of them. They're going through the same crap you are and are probably the only people you will have regular contact with who truly understand your frustrations. On the other hand, knowing who you can and can't trust for good cross-cover, sign out, etc. is crucial!!! (I've been on service for 2 months in a row with another intern who I have to do anti-sabotage rounds on--any order he writes is bound to be written wrong/harmful to patients/confusing to nurses=me getting paged at 3am to fix a catastrophe unless I go back and redo his work.
It's a pain in the @$$, but he's a known liability. Fortunately, the CR's know and the word is moving up the ranks. )
Oops--this turned into a little bit of post-call griping mixed in with advice, but read between the kvetching and take the rest with a grain of salt.