I'll blind call on occasion. Especially this time of year when there is still leaves on the trees which limit the range of sight. In fact I've had 3 young bucks respond to blind grunting so far this season. As adams mentioned there reallys isn't an exact way to do it every time. I will usually let out a couple grunts ever 20-30min unless I spot movement in the distance. Then I might grunt once or twice to try to get the deer in closer.