Look through magazines and catalogs for ideas. Don’t be afraid to draw sketches. Lots of them. They don’t have to be artfully rendered, of course. But remember, the more detailed your sketches, the more useful they’ll be. Grab some graph paper, the kind with four squares to the inch.
Start by penciling in room dimensions to scale, such as 1/2"=1’. Now fill in the fixtures. Just trace the patterns here. Put in doors, windows and closets. Then, visualize how it will look for real. It might even help to stand little cardboard walls around the layout for perspective. Be creative. If you don’t like it, you can always start over. It’s an architect’s prerogative.
When you draw your layouts, the National Kitchen and Bath Association recommends these dimensions:
21 to 30" of room in front of the lavatory
15 to 30" from the center of the toilet bowl to the wall or fixture on either side
21 to 30" clearance in front of the bathtub or shower
Also, don’t forget to allow for doors and closets swinging in.