Your goal as a student should be to maximize your learning time in the ED. I suggest to my students that instead of setting a goal for total number of patients, set a goal for new lessons learned daily, whether these are your actual patients or not. In general these are pretty reasonable guidelines:
2-3 procedures per shift (lac repair, abscess I&D, LP, etc) depending on the level of comfort of your attending and their time to supervise.
2 Critical Patients per shift with the preceptor (shadow, observe, and work on presentation).
The remaining time should be spent learning about those things you have not seen before, including those being managed by other people. Don't get in the way, but learn by watching. You have been given two ears and one mouth - use them proportionally.
Your biggest goal as a student should be to get a real handle on the top 20 EM complaints (Chest Pain, CHF, Abdominal pain, sepsis, etc) and have a framework for why and how to work these patients up. You should also focus on communicating these as efficiently as possible, using as many "buzzwords" as possible to get your point across to those listening to you.
Pay special attention to how the attending or preceptor communicates with consultants and admitting physicians - this will give you a good goal to aim for.
Try to present all of your patients in two brief sentences or less, using pertinent language as much as possible. I.E. "Room 4 is an 86 year old lady with abdominal pain, nausea, vomiting, diaphoresis, and pain out of proportion to examination. I'd like to order a CT, Lactate, keep an eye on her pressure, and have you take a look." or something along those lines. Then, you can listen to the attending present the patient to the surgeon using even less verbiage "I have a lady here with ischemic bowel." That's a great way to tie it all together...