Learning how to be organized is an important life skill, so help your kids develop it early in life by creating designated storage areas for books, crafts, and games, and making sure they put their items away when they're done using them. This task is made easier with the use of baskets and boxes labeled with each child's name, or the specific items they should contain. At the end of the day, they know exactly what should go where, and they can simply dump items in the right basket.
Also, keep in mind that kids respond better to rules when they're made fun. Find storage bins that are colorful and playful (ie sports themes or animal themes) to make cleaning up part of the fun.