Most houseplants seem exotic to our eyes because they originate in tropical rainforests, rather than in more northerly environments. Bromeliads, split-leaf philodendrons, orchids, and their compatriots in the houseplant section at the local nursery can tolerate the low light conditions in your living room because they are adapted to growing beneath the dense canopy of massive evergreen trees in the tropics, where very little light reaches the forest floor.
Yet there is one other thing tropical plants are used to that a living room usually doesn't provide: high humidity. While the bathroom may not be the first place you think of putting houseplants, this highly humid environment is probably the best possible location in the house. Your plants will be happier and you will have a lush, luxurious instant makeover for what is usually the most neglected room in the house.
The Hardware - Containers, Hangers, and Shelving
One reason we don't think to put more plants in the bathroom is they aren't typically the most spacious rooms in the house. If you're lucky enough to have more than 100 square feet of real estate in the bathroom, you may have a few square feet of floor space to devote to a larger potted plant or planter. But if your bathroom is of more modest dimensions, you have to get creative in order to fit the plants in.
Hanging baskets and other hanging planters (they come in all shapes and sizes) allow you to colonize underutilized vertical space with foliage - these are best for vines, ferns, and anything else that grows out more than up.
Shelving for plants can take several forms. One option is to install simple wooden shelves on any available wall space. Or, set a couple of shelves into the casing of the bathroom window, making sure you do it in a way that allows the shelves to be removed easily on cleaning day. This creates a nice scrim effect in front of the window and is perfect for nestling tiny potted plants along with other decorations or practical bathroom stuff.
Finally, don't neglect the shower and tub area. A high, mantle-like shelf (made of something waterproof) is another opportunity to place a few specimens. You don't want the soil in the path of spraying water (that would be too much moisture), but you can certainly place a vine on the ledge and use small hooks along the top of the wall to guide the vines around the bathtub or shower stall. They will feel right at home with their leaves getting sprayed on a daily basis.
The Software - Plants
Now that you have an idea about the infrastructure for your bathroom botanical garden, the second part - choosing and setting up the plants - is fun and easy.
When shopping for houseplants, the label will generally say something like "tolerates low light levels" or "needs bright, indirect light."
These are your best candidates for the tub/shower stall or anywhere that the natural light is blocked by part of a wall or any other feature in the bathroom. They'll also work for north-facing bathroom windows or places where a large tree or another building blocks the majority of the sunlight coming into the bathroom window.