Not too long ago, a bathroom was never part of a house. People went completely outside to do all washing, cleansing, and excreting types of activities. Now that our cleansing goes on IN our house, it's important to pay attention to the feng shui of this room.
The feng shui of a bathroom can be tricky. While in a bedroom you can move around your bed and dresser with a bit of effort, you can't just move around a toilet or sink! They are where they are for plumbing reasons. So tweaking the feng shui of this room can take some additional creativity.
There are two main keys here, which are critical not only for feng shui but also for general health. Keep the toilet lid down. Keep the door closed. Why? Remember what you use your toilet for. You absolutely want that lid closed BEFORE you flush so the bowl contents do not aerosolize into the air you breathe. And you want to leave it shut for the same reason.
Keep an open window for the same reason. If there is no window there, use a mirror to give a virtual window.
There's clearly a lot of water energy in a bathroom. Counteract that with earth style energy. Pottery, crystals, and other similar objects can help provide that balance.
It's critical to keep a bathroom clean. It doesn't take that much energy to do it, and the rewards are many.
Finally, think about adding a plant and a gentle night-light to your bathroom.