Use pedestal sinks instead of large vanities, as these take up less real estate in the bathroom and create free space.
Paint with light, soft colors to make the room appear brighter and more open.
If possible, lay tiled floor diagonally, which will make the floor appear larger
Put toilets in corners to take up as little space as possible
Avoid putting things in the way of the door swing. If your bathroom is really small, have the door swing out so that it doesn't collide with anything in the bathroom.
Glass shower doors allow people to see into the shower, which will make the room appear larger (as opposed to a curtain, which will act as a wall and essentially hide whatever is behind it).
