i think the best thing i have learned over a couple of years of being super skint just when i needed new clothes (post babies, back to corporate) is divide and rule. Primark and uniqlo sales and maybe tesco/asda sainsburys to get: skinny highwaisted jeans, stretchy jersey tops, plain skirts (uniqlo skirts amazing) underwear if possible (depends on boobs, but I think primark bras quite underrated!) Primark do plain long sleeved scoop neck jersey tops, plain long 'dress' vests (obv a dress if you are a skinny 16 yr old: a top on me!) and ordinary length vests. very useful to have all of these in navy, black, grey and whatever else you like. In fact you can do capsule wardrobe in very basic colours: black, grey, dark blue jeans. navy/black/grey cardigans. THEN I add in cheap fashion, so any of my jeans might go with a little lace-edged vest from asos like this: plain black lace top but I got it on offer.
I really unashamedly know what I like now, like little cream tops with the jeans and the dark cardi. I'm sure if you look at me you'd think 'god she has very pared down, simple taste' but it's really just to make it all mix and match and go further and be cheaper! Esp for an office.
Then shoes: if you look around there is normally something in style that is cheaper, like you might not be able to get expensive trainers for every day, but superga or similar plain lace up gutties very cheap (also primark etc will do them). Plain black pointy shoes or whatever you like for evening or work. I think Asos amazing for cheap stylish shoes.
Then trying to add fashion: once I have this very plain, pared down (boring but perfectly stylish) look down, I add cheap tops on sale that are a bit more on trend, or a little bag or something, but again I sort of now know what things go together.
Not to derail the french chic thread onto this one, but I quite often look at things and think 'would my chic (imaginary) Parisian friend buy these?' inspired by living in France where in my experience they seemed to be both thrifty and happy to consider a purchase in the shop for a long time to check they liked it and it worked for them. Thus getting away from the panicked supermarket sweep effect.