Depends on the helicopter you deal with. All three of the life-flight organizations I have dealt with, not to mention the military helicopters I have utilized on SAR missions, all want the same thing:
1) Wait until flight crew calls you on pre-planned hailing frequency. Take the time to arrange the frequency via your dispatch when they launch the heli.
2) When asked, use a single patrol vehicle's lights for a short duration until pilot advises he/she has located your position.
3) Turn off ALL lights, and instruct all ground personnel to maintain light discipline.
4) Let the professional aviators do their thang.
Another big, big, BIG note: Make sure nobody decides to bust out their personal camera for a fun nightshot of the helicopter landing. One SAR mission last year nearly turned deadly when a volunteer decided to light off a big camera flash directly at the cockpit during the touchdown. The pilot had just rested the back part of his skids when he was completely blinded by the camera flash. His NVGs took a full five seconds to recover from the flash, the whole time he was blind. Needless to say, our SAR team had a lesson on playing nice with the helicopters. The pilot later said he thought the camera flash was from his tail rotor exploding against the ground and flaming out the engine. His pucker factor was pretty high.
I know it seems obvious, but take the 30 seconds to brief everybody around your LZ before the chopper lands. Lots of people suddenly want to help during the landing phase, and that usually entails flashing bright lights toward the helicopter. It's common courtesy to your flight crew to keep everybody on the ground dark.
My .02 cents. Exchange rate varies