Marble is a beautiful but porous stone, which means it needs a little extra care in a wet environment like a bathroom. The most important step is sealing: a quality penetrating sealer should be reapplied roughly once a year (more often in high-use bathrooms) to keep water and soap residue from soaking into the surface.
Day to day, wipe up standing water and spills quickly rather than letting them sit, and avoid acidic or abrasive cleaning products - lemon, vinegar and many general bathroom cleaners can etch marble over time. A pH-neutral stone cleaner is the safer choice.
Using a bath mat near the shower or tub also helps reduce constant water exposure on one spot. If you already have marble that's showing dullness or light etching, we can advise on professional polishing to restore the surface rather than replacing it.