Replace the tile in your shower with new tile in a more contemporary style. Many older bathrooms have tile that can look somewhat dated, like pastel colored tile or tile with a floral pattern. For a more contemporary look that will easily fit in with stylistic changes, look for a solid color that can blend with many different styles of décor, like blue, green or black. As an alternative, checkered Bowery-style tile will blend with both contemporary and antique fixture and accessories, as will some types of natural stone like marble, granite or travertine.
Put a new layer of grout around the tile in your shower. After regular use, the grout that holds your tile in place will take on a dull, somewhat dirty look. Going over the grout with a fresh coating can be done fairly quickly and it can make your whole shower look newer. If you are unsure of your ability to re-grout your tile, consider hiring a professional to do it for you.
Get a new shower door made out of a more contemporary material. Replace the shower door with a clear or block glass shower door if you have a traditional frosted glass shower door. Look for a thinner frame than traditional shower doors, or use a shower door without a frame if you are going for a very contemporary look.
Swap out your old shower curtain and hardware for new ones -- if you don't have a shower door. This gives you a chance to update your style in the bathroom to current trends or to go with new fixtures and accessories without spending too much money. As an added benefit, a new shower curtain and hardware will make the bathroom feel cleaner and fresher.