This is a personal preference.

Personally, I put my draw-hand thumb at the base of my jaw bone with the " big" knuckle of my index finger essentially in my ear hole. On top of that I put the tip of my nose on the string. These things in conjunction with a peep gives me 4 points of reference.

If you are interested in some good reading , take a look at " Idiot Proof Archery" by Bernie Pellerite.