How many patients is a full load in your ER?
You really have to prioritize by ABCs - airway, breathing, circulation. Anyone who is trying to die more than your other patients comes first. Anything else is a nicety, not a necessity. Pain complaints make up about 70% of ER visits, so learn how pain is managed at your place - do your docs start with non-narcotics? Is IV acetaminophen (Ofirmev) available? That stuff is typically amazing, but is pretty expensive so not also carried everywhere.
Don't do a head to toe. Focus your assessments. But I did get in the habit of listening to lungs/heart on everyone, it just takes a minute and is good practice. I obviously add in bowel sounds on belly complaints.
If a patient tells you that they feel like they are going to die, believe them. Get EKGs on little old ladies with abdominal pain or who just don't feel well - I have caught a few STEMIs that way. Keep your patients on the monitor and learn how to set up your monitors to cycle BPs at appropriate intervals so you aren't caught without vitals.
You are going to feel silly and slow. Doesn't matter if you had 10 years of ortho/med-surg. That's just what happens when you go to the ER from anywhere else. Are you getting constructive feedback from your preceptor? How do they tell you that you are doing? Probably better than you think you are.