After placing all upper cabinets, begin installing the bottom cabinets, starting at the high spot of the floor. The high spot is usually the corner or one of the end base cabinets. Measure to make sure there is enough room between upper and lower cabinets, then drive screws through cabinet back into the wall. If lower cabinets aren't level, use shims to level them (Image 1) and raise them up to the high point. Check for level on bottom cabinets front to back and side to side. Once the cabinets are level, drive screws through the cabinet back into the wall (Image 2). As with the upper cabinets, secure adjoining cabinets together with screws (Image 3).