Remove everything from the closet so you are able to see how much space you have to work with and start with a clean slate.
Look through each item of clothing. Consider whether you have worn it in the past year or not to determine if it's something worth keeping. Some items like formal dresses or coats may not be worn frequently, but you'll want to keep them around for formal events or inclement weather. Keep that in mind when deciding what to keep and give away.
Donate anything that looks dated or no longer fits. If items look too worn to donate or have stains on them or holes, throw the items away. Look through all of your shoes and accessories to determine if they're worth keeping, or should be donated or tossed away.
Put the items you're keeping back into the closet. Organize clothing by function to help you easily find wardrobe options. For example, group pants, dresses, blouses and T-shirts together and hang them on the rack in the order they are most used. This will keep the items you need on a daily basis toward the front and center of the closet.