Even small switches can have a big impact, giving you a feeling of control and order (in one personal space, at least!):
No wire hangers!
Joan Crawford was right. They make weird dents in your tops, fight with all the other hangers and can't hold anything substantial. Go for wood or padded hangers—ideally, only one kind—and point them in the same direction, for visual harmony. To make it even more orderly and pleasing to the eye (and, therefore, your psyche), arrange clothes by type (tops, pants, etc.).
If you keep shoes on your closet floor, line them up, grouped by color or style. If they still tend to wind up in a heap, use an over-the-door rack.
Grab a hammer and nail and install a pretty but sturdy hook on your closet door, or on the wall next to it. Use it for your just-ironed or freshly dry-cleaned clothes; when they're not wedged between other items, you don't have to worry about wrinkling.
Keep a small trash can close
This provides a place for price tags and plastic doodads. The fewer there are to stick to your feet, the saner you'll be.