Airstarts have many bad possibilities, mostly involving the diversion from the job of maintaining a good autorotation. Crowding an airstart into an off-site emergency landing is liable to produce a case where neither is done well, and a fatality is the cost.
Best method, memorize the steps so that you can say them in the shower automatically, run your hands thru them while sitting in the cockpit (and perhaps holding the cyclic in your knees!) and then enter auto while in typical cruise, and practice running your hands thru the mock re-start while maintaining an auto glide to a prospective landing spot. This practice is golden, and should tell you if you have the ability to attempt a real one.
If the engine conks out, for real, don't dare try a restart unless:
The above practice has been impeccable
The situation is not pressed (enough altitude, an easy landing spot, an easy glide to it)
The engine failure cause is reasonably known ("Ouch, I forgot to switch tanks!", or "Gosh, I twisted the throttle closed too fast!")
You are feeling lucky.