One method is to use shelf dividers to separate the wider shelf into multiple narrower shelves. Think about these dividers as being similar to book stands that separate books in a library. These dividers will help you to partition off your wide shelf and will give added support for items that have a habit of leaning over to the side such as clothing, linens or other bedding.
Another type of closet shelf that can be used is called the half-shelf, which only takes up space at the front half, leaving an empty space at the back of a deep closet. This shelf leaves open space at the back to help you store tall or long items much easier while still making room for storage shelving.