Some people like the idea of dividing even a small vanity with cabinet on one side and drawers on the other. Larger items can be stored in the cabinet and small items can be organized in the drawers. If you have small children, you can also place locks on the drawers used to store potentially dangerous items and cleaning substances.
If you are planning shelves for storage in your new bathroom, consider building shelves that are recessed into the wall. These shelves can be either framed with trim or left unframed. Or you can add doors to keep things on the shelves dust free. In a small bathroom, doors with glass or frosted glass doors will make the room appear more spacious than solid wood doors (and frosting creates enough blurring that you don’t need to be quite as neat). You can use the shelves strictly for storage or you can mix storage and display of decorative items. If you cannot or do not want to build recessed shelves, you might consider installing glass shelves. Because they are clear and reflect light, they do not make the room look smaller, as wood shelves might do.