Clean your toothbrush holder frequently
Clean your toothbrush and your toothbrush holder frequently. Regularly cleaning them will clear your items from dust, germs, and dried toothpaste. Depending on the holder, you could put it in the dishwasher, wipe-down with sanitizing wipes, or use soap and water.
Remember keeping your toothbrush clean helps your oral care as well. The most sanitary way to store your toothbrush is to keep the toothbrush in a clean holder where airflow can dry the toothbrush. Yet, it won't be contaminated by bathroom germs. Maintaining your toothbrush, storing it in a sanitary way, and cleaning your toothbrush's holder will prevent bacteria buildup and won't damage the bristles.