Try to align the holes on your shelves with the marked studs on the wall, as screwing them to a stud will make them more secure. Start with the middle screw first, and then use a spirit level to check the shelf. Then drive in your remaining screws. When you have your bottom shelf in place, you can again test out the height of the items you’re going to place on it. This lets you make any last minute adjustments or just get a better idea of how it will end up looking. Install your remaining shelves, leave 4 to 6 inches of wall space between the tallest item and the shelf above it.