Combination of what others have said, FIRST identify if the waterhole/tank is being used. If there are fresh tracks look around the water source and locate where they are accessing the water from, find the trails in and out. Read the wind as it currently is but also what it will do in the evening and morning ( Thermals ). Last find an good concealed spot/ambush point that is close enough for a solid shot but not two close ( think 30-40 yards ) that there is no way a few cows will not bust you when they walk by. The bull will bringing up the rear most of the time. Then range some landmarks so you do not need fiddle with that at all when the time comes. Sit and watch chipmunks laugh at you.