Clear it Out
Distinguish clothing and shoes that you wear and items that you need to get rid of. You can do this by the golden rule of closet organizing: If you haven't worn it in a year, make a pile to bring to those in need.
Also, if it doesn't fit you well, it is time to get rid of it. Instead of hanging on to your "skinny jeans" until you hit the gym, donate them. Then, when you get down to your goal weight, treat yourself to a new, pair of jeans.
If you are on the fence about an item, "flag" the hanger. As you wear each item, remove the flag. At the end of each season, items that are still marked with a flag should be donated. If the item is in good condition and/or if you paid a lot for it, think about selling it at a local consignment store or online at a site such as eBay.
We like to invite our best friend over to encourage us to get rid of clothing that haven't seen us a wear.
Once you have whittled down your wardrobe, you need to assess the layout of your closet. Measure the space you have, making sure to utilize backs of doors, floor space, and all interior walls. When you go to shop for boxes, bins, and other necessary space-savers, make sure you have your closet measurements in hand.
Use every square inch of your closet. Hang shoe racks on the back of your closet door. Classic belt hangers with multiple hooks are also a good solution for hanging camisoles, bras, or scarves.
Get Hung Up
Remove all wire hangers (they don't properly support your clothes) and plastic dry-cleaner bags (they don't allow fabrics to breathe, keeping the chemicals used in dry cleaning in your clothes). There is no way to make a wire hanger work in your space; no matter how organize your closet is, wire hanger lead to a sloppy look.
Save time in the morning by coordinating your wardrobe. Sort by color, and hang like-types of clothing together (i.e. skirts, pants, blouses, etc.).
Sort sweaters, T-shirts, and other folded clothing by color as well. Always remove sweaters from hangers and fold them. Hangers will ruin the shape of sweaters over time.
Store sweaters on shelves in manageable-sized stacks using sweater dividers to keep them from turning into leaning towers of Pisa. Even better, store them in sweater boxes with well marked labels.
Move any snow boots, rain boots, or other "outdoor" gear to your front hall closet (or mudroom if you are lucky enough to have one); restrict what goes in your clothes closet to dress shoes only.
It's possible that no matter how much you try to edit and organize, you just have too much stuff to fit in your closet. If that's the case, then you need to resort to a seasonal system by rotating your fall/winter clothes with your spring/summer clothes. Covered clothing racks can be filled with out-of-season clothes and kept in your attic or basement or under your bed. Flat storage boxes can serve a similar purpose.