Installing Bathroom Cabinets: To ensure proper installation make sure the walls to which you are installing the bathroom cabinets are not only smooth and 100% level but also spotless. To make sure it's level, rest a straight long edge against the wall and make a mark by any uneven areas.
During the installation process you may need to put shims ( term used by builders ) or wood shingles under and / or the back of the bathroom cabinets as you deem appropriate in order to make any necessary adjustments that may be required.
You can use a scribe rail for irregularities that you feel are very significant. Fasten all upper cabinets tightly to the wall studs to ensure they are securely in place, especially if they will be filled with lots of weighty items including bathroom appliances, jugs of bathroom cleaners and bales of tissue paper.
B e sure to drive screws through the cabinets support rail which normally runs right across the back of teh cabinet or through a sturdy ares of the bathroom cabinet. Be sure and use at least 3 to 4 screws for each cabinet, and ensure they enter the wall studs by at least 1 and ½ inches.