There are several options for storing shoes in your closet, the floor should not be one of them.
* Angled shelving. - A shelf tilted on an angle with a rail or shoe stop to prevent them from sliding off. This allows for better visibility and adds a nice design touch. The rails can be done in a matching material, a metal or an acrylic. There is no adjust-ability.
*Flat shelving. - Shelving spaced closely together allows for the homeowner to store a greater number of shoes. The shoes can be placed with the toes faced forward, or altering heel toe to get additional yield. The shelves can be adjusted to accommodate different heights, as well as spread further apart for stacking boxes.
*Cubbies. - Small boxes that compartmentalize each pair of shoes stacked on each other. (I'm not a fan of this one)