When you’re mounting something on the wall with keyhole slots, lay paper over the slots and make a template by rubbing with a pencil. You'll want to make sure your paper is level across the top of your shelf or picture frame. This way you can then level your template on the wall, and you’ll know precisely where to position the screws. This method can work with almost any mounting method if you have something long enough to go between the screws. Sometimes I'll use a piece of foil if it's a longer frame!!!