You go for the things that are life-threatening first, or have the potential to be.
Any problems with respiratory system would be a the top of the list.
Simple example: You get a multiple trauma patient into the ER. Injuries are open fracture of tib-fib, right hip fracture, collapsed lung.
Your first priority would be a chest tube, then the open tib-fib because that is considered an emergent procedure, with the hip to follow, as it could actually wait a few hours.
Hope that this makes it a little easier for you to understand.
Good luck on your exam......