Man, I am screwed for picking a spot. Some have said pick a tuft of hair, others have said pick a dark spot or shadow, and still others have said pick a ridge in the muscle. Man, around here all we have is fat unsculpted, but well groomed deer that only come out on overcast days!!!

I have a little reminder on my riser that says:

P
A
S
A
F
T

It stands for "pick a spot and follow through." As others have said I envision where I want that arrow to enter to hit the exit hole and bury my pin in that spot until I release. It hasn't failed me yet (other things have, but not that).