ooh my favourite topic...
I did this a few years ago and here's how I did it.
DO NOT chuck stuff out first- if you have a separate area (back of bedroom door for me) get out 10 items- mix of tops, bottoms and dresses (whatever is your preference) wear only these 10 items for 10 days- making them into different outfits. I took photos of myself to look at objectively later. Keep a running list of what you wear, how it makes you feel etc. If during these 10 days, anything feels uncomfortable, you don't like it or it's broken beyond repair, put it in a donate pile. (obviously not the broken stuff) At the end of this 10 days, if you still like all 10 items, great- put them in a 'definitely keep' area. Then , get another 10 items out and start again. The key to this system for me was no laundry- put stuff in the donate box as you discard it- put stuff in the definitely keep box as you take it off. That way, stuff doesn't go through the laundry and get all mixed back in. You can then work through a fairly large wardrobe systematically and you are also learning how to capsule as you go along. I have all colours, no beige white and grey here- and no big outlay at the start. I found a huge wardrobe sort too overwhelming so I did it this way incrementally and it really worked. Another good tip is to find an empty suitcase or vacuum bag and store all winter clothes for now, you can then repeat this process in Sept/ Oct. Also, stash away any evening wear etc - divide and conquer is the way to do it- if you work this system through, eventually- your wardrobe will be empty, you will launder your definitely keep box and pop it all in your wardrobe- and Voila- capsule wardrobe ready to go. Don't be bound by number of items necessarily- if you have 4 pairs of black trousers and you love them all- maybe you could store 2 away and keep 2 in rotation- that way, when they need replacing, you have ready replacements. I have a wardrobe of 35 items currently but am scaling down again.