My first piece of advice is to replace all of the doors. At my house, I replaced the mirrored closet doors with simple, full-length brown curtains. My husband wanted to keep one of the doors, but we realized that it looked very awkward. It's a vast improvement. You can use a simple solid curtain, like I did, or find a patterned panel that really catches your eye, like these Ikea Jorun Lov Curtains ($60).
Replace Doors With Curtains