After deciding how far apart I wanted each grid, I measured from the bottom of the grid up and marked the spot. I wanted mine spaced 8 1/2 inches apart, so I measured 8 1/2 inches from the bottom and marked it across the entire piece.
To attach the grids to the windows, I purchased double-sided/mounting tape from Ace. I placed one piece on the back of the top of each vertical stile. On a few I attached them to the outside horizontal stiles.