Reflect the Space With Mirrors
If your space will hold it, get a larger mirror to place in front of the bathroom sink. The mirror will reflect all the light in the room, and pick up the color and pattern. You might consider a collection of mirrors arranged artistically in the place of one large mirror.
Choose a Light-Colored Flooring
Just like with the walls, the floor will appear to open up if it's done with a light color. If you cannot replace the flooring, choose a large, light-colored rug over your existing flooring.
Cut Out the Small Accessories
There's nothing like clutter to make a small space feel even smaller. Pare down on towels and use just one large floor rug. Select one piece of art instead of lots of small pieces. Use one decorative accessory instead of lots of small ones. Store whatever else you really need out of sight.
Get Rid of Any Visual Obstructions
Trade a frosted-glass bath or shower door with a clear glass one. Or eliminate the door altogether and install a shower curtain that can be pushed back to one side when not in use. You'll be able to see all the way to the back wall. Your eye won't stop at the door and think that the room is smaller than it is.