Lots of labeled storage. This ensures that everything has a home so it can easily be put away where it belongs, especially if children are involved. Clear plastic bins and jars are great because you can see what is inside them or at the bottom without having to dig through it and make a mess.
Use pretty curtains to cover shelving units to keep everything out of sight if you have a less than perfect organization system. They're nicer than cupboard doors because you don't have to worry about them jamming or not shutting properly. And if you hang them up using velco you can easily create a few different sets and change them out when the mood strikes.