WHile DD was growing like a frigging weed, I would set a budget, and DD (15) has to buy all essentials from that budget - but I would specify that at the end of the shop, she would have to have:
Underwear
Nightwear
2 pairs jeans
1 pair smarter trousers
3 shirts
a coat.... etc. etc.
Otherwise she would buy superdry and hollister and not have any undies!
I would sit and drink coffee or go to a movie while she shopped and decided what she wanted. SHe had to figure out whether she could afford it all. Then we'd go round and buy the items.
This meant that she could buy lots of Primark basics, and then splurge on a hollister T shirt or some ridiculous pair of shoes.
SHe has now pretty much finished growing, so the budget may be reduced a little.
I do buy her school kit, and decent trainers. I also buy a pair of boots in winter, depending on the state of the old ones. Never scrimp on shoes, and basic shoes do not impact the budget.
Now my son is just starting to grow, I may do the same thing with him. It gives them some idea of budget and value, but allows them to make their own fashion statement, while actually coming home with enough clothes to last them.
Anything outside of basics come out of their pocket money.