In my experience most new hire ED nurses, especially those without EMS or intensive care backgrounds, are "too nice." If someone started out new and was already getting crispy I would wonder why they want to care for people. The "ER voice," "Mom voice," or what ever else you want to call it will develop with time.
Similarly almost every new hire ED nurse takes time to keep up with the pace, this includes nurses with EMS or intensive care backgrounds. The ED isn't like any other care environment and takes time to learn. Almost every new hire we have had gets up to speed pretty quick; those who don't are often nurses who find more value in the type of patient care that can be given in inpatient units (longer relationships, more personal care, et cetera) and often want to go back to those environments. Just like long term care, med/surg, intensive care, et cetera many nurses have tried an environment that they didn't like and there isn't a reason to stay somewhere where you are unhappy. In regards to the occasional new to ED nurses who haven't wanted to stay in the ED, we are happy to work with them to find an environment that they are happier in and find their own personnel success.
I think that most of the tips and tricks you will pick up from your preceptors, however I do have a few thoughts.
Get down to what really matters, in the ED we are all about focused assessments and generally speaking only those who cannot easily articulate a good history are likely to have any kind of head to toe assessment.
Pay attention to what your preceptor is teaching you, and understand that there are many things that are very different from inpatient units (and even ED to ED). For example on adults unless there is a history of transfusion reactions in my ED we never put blood products on a pump, typically we just adjust the roller clamp so it takes about an hour to go in (of course rapid infusion is a whole different topic); this would never be tolerated anywhere else in the hospital. We give zosyn over 30 minutes rather than 4 hours, and rocephin over 3-5 minutes which I think they give over 30 minutes upstairs, and so on.
Understand that patient care is always our most important priority, but we also need flow to take care of patients from EMS or in the waiting room. Sometimes we don't get our patients food trays, give them bed baths, et cetera because we know that the floor can take care of this and we need the bed open. We are not trying to "dump" on the floors, but be able to provide care for the patients who have not yet been medically evaluated.
Most importantly be confident. I don't believe in 'fake it 'till you make it' type behaviors, but have confidence that you will be able to care for you patients, get that IV, and make a real difference. Getting fast while providing good care takes time, just like it did for every other ED nurse.