I was once called an "expert" at taking one-timers by a former minor league player who was coaching some kid, I was flattered, and here are some pointers that might help:
1)Equipment- for some reason, the Drury style curve is my favorite normally but I prefer the PM9/Forsberg for one-timers of different types. The truth is that a flatter blade with less rocker will be more forgiving on this type of shot. Also, I prefer a stiffer stick, if one-timers are likely to be my central shot.
2)Do not forget the importance of rolling your wrists on the follow through. You'll be amazed by how many players forget to do this on a one-timer.
3)This shot is HEAVILY based on agility, perhaps moreso even than strength. Agility because you have to feel great on your edges to drill a one-timer that is not perfectly square.
4)On poor passes that are likely to result in less than ideal shots, try to keep it low. This will ensure higher striking accuracy and allow you to have more control over the shot location (relatively speaking).
5)Do not try to one-time bullet passes. I have pretty darn good hand/eye in every sport, deflections in hockey especially, but since even the world's most elite snipers have trouble one-timing overly hard passes, you/I'm not likely to be great at it either.