There are obvious things to get rid of:
Things that are too small.
Things that are too big.
Things that don't fit you right.
Things that are worn out.
Things that are damaged and can´t be repaired.
Things that don't suit you.
Things you have any negative feelings about.
But there are also things that we hang onto that we shouldn't:
Things you don't wear but you are hanging onto because they were expensive or because someone gave them to you and you think they might be insulted. If you are not wearing them they have no place in your wardrobe!
...that probably covers all the things you don't wear, but I am going to go further and tell you to get rid of some of the stuff you do!
Anything that is very similar to something else you have (I had 2 wine shirts!...we buy something we like, we like it, so we buy something similar...but you can only wear one at a time...so no need for two!)
Anything that required pairing with something specific. (I had two knitted jumpers that had panels where you could see through, so I had to wear a specific colour top under them...so if the matching top was in the wash, I couldn't wear the jumper until it was back...no room for that kind of limitation in a capsule wardrobe!)
Anything that requires specific underwear. (I had a few spaghetti string and racer back tops, if you are not comfortable having your bra straps on show and you don´t have a comfortable, versatile multi-way bra, things like this have to go)
Anything that requires special treatment, like hand washing or dry cleaning (I had a silk top that spent a lot of it's time at the bottom of the laundry basket, waiting to be hand washed, and then when it was finally clean, I didn't wear it because I knew I would have to hand wash it afterwards)
Now here is where I get serious:
I like to be able to wash everything together, so I only have to put one wash on and I can get all my clothes back sooner...so to that end, I advocate cutting out white!
You want everything in your wardrobe to match so it is interchangeable, so you need to make a decision between black and navy...I chose black. Get rid of everything that is the other colour.
Lastly pick the most versatile of what you have. (I had a light pair of jeans that was by design distresses and a darker pair without any rips. I didn't wear the lighter pair in winter, and couldn´t dress them up as much, whereas darker ones fit in year round, and plainer means they go with more things!)
This should cut down your wardrobe quite a bit...but where to get rid of them is a whole other blog post (as is exceptions to the above rules...see previous post....What To Keep (when you are paring down))