1. Hang It Up
Some of the best, and most easily accessible, bathroom storage is on the wall or the back of a door. Fasten a few decorative hooks to the wall and you can easily make room for hanging up many more towels, robes or other items (see this article for instructions on hanging hooks). Hooks can also be fastened to the door, although the hollow-core doors often used in homes these days really don't much for a screw to bite into. In that case, buy a hook or two that just hangs over the top of door -- no screws involved (see photo).2. Get Inside the Wall
There is usually a wealth of potential bathroom storage space sitting inside the walls. The typical bathroom wall has 1/2-in. drywall attached to 2x4 studs, spaced every 16 inches. Those studs are 3 1/2-inches deep, which is plenty of depth to install a built-in shelf.This is a fairly easy DIY project (see photo). First, decide where you would like the built-in shelf to be located. Next, find the two studs in the wall that will frame the sides of the shelf. (Not sure how to find wall studs? Check out How To Choose and Use a Stud Finder.)
Now, carefully cut the drywall to open up the wall. Finally, build a basic shelving unit to fit inside the opening.
3. Store Only What You Need
Many of the items we keep in regular bathroom storage really don't have to be there. So find another place in the house to use as backup bathroom storage (see Top 10 Overlooked Storage Spaces for some suggestions).If you are a Costco or Sam's Club shopper, for example, you may periodically pick up a huge supply of toilet paper. Keep a few rolls in the bathroom, but store the bulk of them in a hall closet, on a shelf in the garage or even under a bed. Likewise for extra towels and little-used items. The fewer things you store in the bathroom, the more unused bathroom storage you will create.

