Mountain rescue technique is not really something I can pass through this forum, but I'll add a few thoughts.
It is dangerous, challenging, diverse, and rewarding. I believe the ideal pilot for this will have plenty experience in Heli-ski, longlining, IFR ops and on-scene EMS. The machine needs a HOGE above the expected rescue altitude, with capacity for the victim(s) and fuel to make the hospital. Also, the helicopter should be able to handle strong wind from any quadrant.
We use a 255' hoist. Ideally we hoist between 35 and 50 feet, but sometimes trees and terrain dictate a higher hoist. If the trees are more than 255', we hoist our rescuers down 255' then they rappel off the hook to the ground. The hoist operator tells us where the site is with reference to the helicopter using arbitrary units that are based on rate of motion towards the spot (ie: "forward and left for 10.....5...4..3.2.1..steady forward and left"). Works really well.
In my opinion, long lining is not an option for any rescue service. The patient is exposed to the environment beneath the helicopter far too long. Hypothermia, shock, fear, treatment delays are just some of the patient concerns. Danger for those on the line and for those in the helicopter is increased (not as likely to pickle a live load). Since the load must be relocated by moving the helicopter, a guide line is not possible thereby increasing danger of swing, spin, instability, etc.
Our mirrors were removed due to cost...some weren't taking care of them properly. Very bad decision, methinks.
As far as training, number one knowing machine and limitations, number two is mountain flying training (recommend Canadian Helicopters...v good course), then knowing area of responsibility and practicing the sequence regularly to make sure you know it instinctively.
There's so much more to talk about. Hope that's what you were looking for.