I spent 20 years as a paramedic before becoming a lawyer and let me tell you this...drivers do the craziest things when they encounter emergency vehicles. This PSA video
from the Tuscaloosa Fire Department humourously and accurately gives you what you need to know when you encounter emergency vehicle traffic approaching you.
For my Denver, Colorado readers, the appropriate statute is C.R.S. 42-4-705. In short, if you are approached by an emergency vehicle operating its lights and/or siren, pull as far to the right as possible and come to a stop. If you encounter a parked emergency vehicle on the side of the road, slow down and move to the farthest lane away from where they are parked to allow for them to move about the scene safely.
If you get specific directions from emergency personnel on the scene that contradict these rules, you should follow those directions.