Pick a shower curtain that complements both the girls' personalities and color preferences. A feminine and girly shower curtain is an excellent choice unless one of them is a tomboy. If they both enjoy the beach, a sea-inspired theme is a wise idea. A shower curtain takes up a large amount of space in a bathroom, therefore it's the first priority.
Paint the bathroom wall in a softer shade of the shower curtain's main color. Another option is to paint it in one of the curtain's accent colors or a neutral shade, such as off-white or beige.
Coordinate the towels, washcloths and bathroom curtains with the shower curtain. In bed-and-bath and discount stores, accessories are often available that match the shower curtain designs. It's a wise idea to purchase the accessories, particularly if the colors in the shower curtain are difficult to match.
Lay down a solid color or themed rug or two in front of the sink, beside the bathtub or in front of the toilet. Choose rugs that are the same color or theme as the shower curtain, or in one of the accent colors in the curtain's design.
Pick accessories -- such as toothbrush holders, cosmetic organizers or wastebaskets -- in one of the accent colors from the shower curtain.
Hang a picture on the wall that enhances the bathroom's theme. For instance, if the shower curtain has pictures of shoes, necklaces and other girly accoutrements, select a print of a teen looking at her reflection in a cheval mirror or dressing for a special event.