First, choose your shower curtain, since it is the biggest source of color in your bathroom besides the walls. Find one with a nice design, although a solid color also works.
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Add new towel racks. Putting them by the bathtub or over the toilet are good, convenient locations. Also, have some places for your hand towels by the sink. All racks should be the same style.
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Purchase rugs for the bathroom floor that match the towel colors. You need at least one rug for in front of the bathtub. Placing rugs by the sink and toilet are optional, depending on the size of the bathroom.
NOTE: If you cannot use a shower curtain in your bathroom, use a patterned rug(s) as the base for your color scheme. You do not have to choose bathroom rugs. I had stair runners made into rugs years ago and use two of them in my master bath. They have held up beautifully.
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Find some unique way to personalize the bathroom. Adding a thrift shop dresser as a storage solution or a sink vanity can really look classy. Collections, such as antique bottles or containers, can be artfully arranged on a shelf as a design statement while also serving as holders for lotions and specialty soaps.