I had planned to really delve into closet organization this month but I'm not sure that will happen with all the Halloween festivities this weekend.
I go through my closet about a couple of times a year but it always seems a mess. I chalk that up to the fact that it is super small (no walk-ins here). The first place I start is by taking all the hanging clothing out of the closet and do a quick purge of anything I am really sure I don't need/want anymore. I then place everything back in the closet with hangers hanging backwards ( the open part of the hook of the hanger should be facing you).
When you wear something, put the hanger back the other way and hang the item on that hanger when you hang it back up. After a year (or even 6 months) you will have a clear picture of what you wear and what you don't making a closet purge really easy.
I got this idea from the great Peter Walsh.