There Are a lot of good Ideas on here to help you out. Me I am a cross between a guesstimater and a pre picking landmarks kind of guy. I usually pick out a few land marks and tell my self not to shot untill the bird is within that place. But mostly by the time the gobbler comes in I am so worked up I forgot all about them landmarks I picked out. and I end Up guessing. Last year I put a Simmons Pro Diamond on my gun it helps a ton. When the bird fills up that rectical he is within 40 yards