"take a deep breath..."
I've been driving ambulances and fire trucks for years now... The most important thing you can do when someone is coming up on you with lights and sirens--before anything else--is to take a deep breath and make sure you're not going to cause an accident. Don't stop dead suddenly in moving traffic. Do slow down, signal, and pull over to the right as soon as you're able.
Mefite paramedics skyl1n3 and itstheclamsname offer pro advice on the question "What do you do when you're driving and an ambulance is coming down the road?"