When you are satisfied with the location, stick an awl through the top screw hole in the standard, punching a small indentation in the wall. This will make it easier to set and drive the screw. I’ve also found that when you poke a starter hole first, you do less damage to the wall when you drive the screw.
Drive a screw through the top hole just deep enough to hold the standard in place securely; don’t make it so tight that you can’t move the standard a little.
Now, set your level alongside the standard, adjusting the position so that it is perfectly plumb (that is, vertical). You’ll be plumb when the bubbles in the top and bottom vials are centered. Poke awl holes and drive the remaining screws home. The standards should be just barely snug against the wall; if you drive the screws too far, you may push them into and thereby damage the wall.
