1. get a good h/p, be thorough
2. BEFORE you present to your resident/attending have a plan of what you would like to do, be prepared to defend
3. take a couple minutes after seeing the patient to gather your thoughts and put together a coherent presentation
4. NEVER check out a procedure to anyone (suturing, pelvics, LP, DRE, etc..), usually we students love to do those things, so it's not really an issue, but sometimes you have those crappy shifts. You just want to leave the ED, but you can't, you have to wrap up loose ends.
5. NEVER just leave when you have a patient that is to be admitted. you need to call the admit team, make sure that they have a bed, and that all is squared away. nothing worse than a resident who just came on shift trying to figure out this patient who has been sitting here for the last 5 hours and explain it to the admitting team. yeah it creates more work for that resident, but worse, the whole shift change time is where the most errors occur, so stay the extra 30m-1h to make sure that your patients are prepared for dispo, set for admission or at a point that it is safe for someone else to take over.
you can take all of this with a grain of salt since i am just getting ready to start residency. I didn't do a "warm-up" EM rotation at my home institution, so i was REALLY rusty when i did my first away at Christiana. It comes back to you really quickly. I did two away rotations last year, used this advice that was passed on to me from this website and got A's/Sups/Honors on the rotations. Remember that the ED is the workhorse of the hospital. typically the residents are pretty well-respected because we work hard, efficiently and love to do procedures. That is what makes the ED and it's staff unique. You likely know that this is what you want to do, so just work hard and have fun. I was scared as hell for my first rotation, it's normal. Just do what got you here, bust your ass.
I didn't rotate at Denver, and thus know nothing about their system, but other "big name" institutions really lay out your role for you. There should be no mystery. The first day they will tell you exactly what's expected. Do it and then some. You will be fine. I loved every second of my two away rotations. I met some great people, learned more in 8 weeks of ED then one year of medical school.