A checklist that the ER is correctly cleaned and equipped, that all equipment is in correct order and in the right place, connected, powered up and configured correctly. That all consumables are sufficient. That the correct combination of staff is present and sufficiently rested for the shift, and that lines of communication and escalation are open. A clear procedure for what happens if something isn't up to snuff, but the ER needs to operate anyway, especially making sure that everybody knows what doesn't work.
Clear checklists for all standard operations. Second pair of eyes and clear unambiguous concurrency from two different qualified members of staff before any medicine is administered or other non-trivial decision is made.
Etc etc etc.
1. http://www.nytimes.com/2009/01/20/health/20surgery.html?_r=0
Checklists have made my life easier. For example, I got in to work today and if I hadn't made a checklist of my daily procedure I might be stuck on HN all day, but just looking over today's tasks I know what my first step and final steps look like so I can begin immediately upon entering the building. If I make a mistake I won't kill anyone, but if my life is in someone's hands I'd very much hope that they are running through a checklist built around the priority of keeping me alive first, and making me healthy second.