ORIGINAL: RobinAim Low
Forget about a rangefinder. Limit yourself to 20 yards or less. It's either in range, or it's not, and only one pin to worry about. Put some markers out if you have to to show a 20 yard radius around your tree. I have killed more deer under 20 yards than past 20 yards and I have killed more thana few, so don't think you are severely limiting yourself that way. Once you punch one right, it all gets easier from there.
Good point there, take it slow and it will all come to ya. And once the first one falls its all downhill from there. Bill Winke wrote an article called "taking the edge off," its a heck of a good read for someone trying to tag their first deer.