Since this room is typically one of the smallest in the house, bathrooms especially benefit from bringing in more light. However, privacy is of more importance here. So, opening up the windows to natural lighting is not usually practical.
You can, however, gain a lot of natural lighting by using glass brick blocks or covering windows with an opaque covering that allows light in while still maintaining the privacy needed. Also, blinds or shades can be added inside the window itself to be drawn when necessary or opened to allow light to shine inside.
Storage is also of utmost importance in the bathroom. Not only do you want to keep toiletries up and out of sight, easy to reach, but you also want to free up counter space. Accomplish this by getting creative.
Use a wine rack to roll and store towels. Swap out a traditional vanity under the sink for an older dresser that has been painted or refinished. Add a lazy Susan inside existing storage shelves to make items easier to access. Whatever changes you make in the bathroom, be sure to get the most out of the furnishings by having every piece serve double duty as a practical spot while providing you with extra storage.