I have kind of done this over the last two years (due to budget!)
First, I spent two different days at big shopping centres trying on (not kidding) about 100 tops and taking selfies to look objectively at what colours actually suit me. Lighting in changing rooms isn't ideal but it made me see how 4 shades of green or cream vs white could make my face look dull or fresh or make my eyes sparkle, for example
Then, I looked at Pinterest and other sites to decide what styles I actually like that suit my shape. I then came up with some key words that describe the vibe of what works for me: eg, yours could be "autumn, a-line, 60's, pattern".
Then I spent a year buying ONLY basics: 5-6 plain t-shirts; 6 trousers - 2x jeans, black jersey, 3 flowy viscose neutral tones; 2 skirts; 4 belts; 4 necklaces from charity shops - two gold, two silver, chunky and delicate of each; cream trainers; black brogues; brown sandals.
I really was starting from scratch!!
Now, for the last year, I've added in more interesting pieces: a couple of coloured shirts, couple more skirts, two jumpers, non-neutral bags, band t-shirts, bright shoes, etc.
All of this is from the high street or charity shops but I have to think carefully before I buy anything: I can't just love something, I have to consider the outfits it could create with what I already have, and it has to fit in with my key words so I know it will earn its keep.
It's been a revelation. I went out at the weekend and felt a bit chilly walking to the car so I popped back in for a jumper: I just pulled it out the drawer in 5 seconds and it hit me that I finally have the start of a wardrobe that is interesting, inspires me and is full of items that work well together and make me feel good.
Edited to say, two years ago I would have gone without a jumper because whatever jumper I had wouldn't have gone with the rest of the outfit or fitted!