Disclaimer: I took a good, hard look at my closet, so some of my advice is extreme. Apologies for the length, but I promise you, this will work!
What you NEED before you start: A Full length mirror!
Pre-work: Plan to allocate an entire Saturday or Sunday to just do this. If you keep work shoes at your desk, bring them home because you need them to try on work clothes with.
On the day of Project Closet Fancy:
Brew a pot of coffee, eat breakfast and then go through EVERYTHING (clothes, coats, jackets, shoes, belt, scarves). (What I did was dump ALL my clothes on my bed. Then sort out summer/vacation/special occasion wear –which you can tackle another day or after you go through fall/winter stuff. Then I went through what was left, piece by piece.)
As you make your way through your clothes, make 3 piles: Trash, Goodwill, Keep (You can also make another sub-category: "?"/Fix). Nothing goes in the "Keep" pile unless it has been tried on in front of that full length mirror. Try on bottom items (pants/skirts) with the heels you'll most likely wear them with (just because a work pant looks good with a satin absolutely not work appropriate pump, does not make it a keep.) AND with blouses/tops. For pants, check out how it fits in the waist and hips (close, but not tight and NO bubble gut effect); look at the break of pant leg with the shoes you will commonly wear them with. For blouses, pay attention for button gapping, worn spots, sleeve lengths and side pilling. Here's the golden rule: ONLY keep the things that you like how you look in. Why? Because if you like how you look in it, you'll wear it. If it has a fray/hole, if that sweater is pilled, TRASH. If it has a hole, but its in the armpit, so you only see it when you lift your arm, TRASH it. You could have fixed it and if you really wanted to, you would have done so already and you haven't. So TRASH IT! Yes, you need a brown pant, and good brown pants are so hard to find and you paid $100 for them at banana republic, but every time you look at them, you think of doo-doo, TRASH! If that pant is in great condition, but you hate how it makes your butt look, TRASH! The more below-par pieces that you keep, but never wear, is taking up the space for those pieces that you'll grab for as part of your go-to outfit. Also if you keep a below-par piece, you run the risk of wearing it on a day when you need to look 100% sharp. Sharp means no pills, no gaping, no tears, no scuffs. Fancy always.
Don't get alarmed if the Trash & Goodwill pile are larger than the "keep" pile because sometimes that needs to happen and sometimes we hold onto things that we have no business buying in the first place: True Fancy Story: I had this awesome long sleeve corset-style blouse in my closet with the tags still on it. It’s a flattering cut, but it's hot pink and satiny! Why did I buy it? More importantly, why have I been keeping it for the past 5 years? Because it fits me nicely and it's pink. But I FINALLY let that blouse go, tags and all because in five years, I had not, nor ever will wear it. Don't even bother with the "if I don't wear it this year, I'll throw it away next year". TRASH it now!
Once you have your piles, organize and hang the Keep pile in your closet using Slimline Hangers.
I organize by item (blouse by color, pants by color, suits by color, dresses by color), but some people organize by color (all blue items, then all brown, etc). Organize what works best for you!