A great way to use often wasted space is to add an over the door shoe organizer such as the one seen here:
These can be used to house office/art/school supplies, small toys, accessories, and of course— shoes. Make sure you purchase one with clear pockets so you can see the contents. These are available for as little as $5 at big box stores.
This one here whipped a bathroom linen closet into shape in no time!