This is a great and exceedingly common question. I'll have much more to say on the subject as YoCP unfolds but for now, here's one strategy that will make facing an overflowing closet a more bearable experience.
Start with ONE TYPE of clothing (let's say pants). Take 'em all out of the closet. ALL OF THEM. And yes, you have to actually take them all out of the closet—none of this picking-through-items-on-hangers business. You'll have a clearer eye and will be much more likely to get rid of items you don't need if you've actually removed the stuff from the closet. Also if they're out of the closet you can put them on to see if they fit and are flattering. But we'll get to that in a sec.
Once all the pants are out of the closet, push the remaining items so that there's a block of empty space on the rod. Now you'll start sorting all those pants you just took out of your closet into yes/no/maybe piles.
- If you wear a pair of pants regularly, it goes in the yes pile.
- If you know a pair of pants doesn't fit, is out of fashion, isn't flattering on you or just is something you never wear, toss it in the no pile.
- If you're unsure, those pants go in the maybe pile.
Now bag up all those no pants and put the bag near the door.
Next put all the yes pants back in the closet, using the space you cleared on the rod to ensure that they're all together in one section.
Now it's time to face the maybe pile. Try each pair of maybe pants on. I know that's brutal, but you gotta do it. After trying each pair on, make a decision about whether or not you're going to keep it. Just like with our initial no pile creation, if a pair of pants in the maybe pile doesn't fit, is out of fashion, isn't flattering on you or just is something you never wear, toss it in the new no pile you're creating. If you decide to keep the pants, put them in the new yes pile you're creating. You'll also want to create a third pile for items that need to be repaired or tailored.
Once that's done, put the yeses back in the closet with the other yeses, and add the no pile to that bag you put by the door. Then get those pants IMMEDIATELY OUT OF THE HOUSE. Donate them, consign them, whatever … just get them out. And on your way out, also take the pile of items that need to be repaired or tailored to wherever they go for repairing or tailoring (if you do your own repairs or tailoring, those items should go into a dedicated bin or basket until you can get to it; if the pants are in there for more than two weeks be honest with yourself about whether or not you're actually going to do the work needed and pitch if the answer is that you're never going to get around to taking in that waistband.)
Now stop. That was a lot of work and you should be happy with what you accomplished. Don't worry about the stuff you haven't gotten to yet, there'll be time for that another day. Already you should be seeing a difference in your closet—probably more room, and also those pants that you put back are clustered together, which will make it easier to pick out outfits.
The next time you feel inspired to take on the clothes monster, do the same thing but with blouses. Or skirts. Or hoodies. Whatever! The idea is to just go one clothing type by one clothing type, which will help to keep you focused and from getting totally overwhelmed by what is a pretty monstrous task.