If you’re installing more than one base cabinet, you will need to make sure the units are level, plumb, and flush with each other so that they will work properly and look right. To ensure this, the first cabinet must be level and plumb, both from side to side and front to back, because all of the other cabinets will be aligned to it.
A corner cabinet should be installed first. Plan to put in cabinets after rough wiring and plumbing but before new flooring.
If the cabinets don’t arrive assembled, put them together according to the manufacturer’s directions, with the exception of the doors, shelves, and drawers. For preassembled cabinets, remove these parts, labeling them to take the guesswork out of reassembly.
The wall to which you are affixing the cabinets should be smooth, level, and clean. Place a long straightedge against it to make sure it’s flat. Mark any bumps or bulges.
During installation, tap short pieces of wood shingles, or shims, beneath and/or behind the cabinets as necessary to make slight adjustments. If the irregularities are significant, compensate for them by using a scribe rail.
Upper cabinets should be fastened securely to wall studs, particularly if they will be loaded with heavier items such as small appliances or big containers of bathroom cleansers.
Most cabinets have a support rail that runs across the back; screw through this or through a strong part of the cabinet. For each cabinet, use at least three screws that penetrate the wall studs by a minimum 1 1/2 inches.