I tend to buy standard stuff with a few odd items.
Standard black jeans, ideally Levis depending on my wealth, polo shirts, idealy Ralph Lauren or Lacoste or Fred Perry is ok as long as you don't buy the chav ones. Wool jumpers, again, ideally one of the traditional brands but happy with cheap stuff aswell and then only a couple of shirts as I hardly wear them
Also doesn't hurt to have an alternative to jeans such as green brown cords or something khaki colour and even a pair of standard adidias trackies.
That way you can always bung a jumper and shirt/shirt with dark jeans and look ok.
And ofcourse a decent coat. Don't actually have a posh one more of a hiking one but no one cares about your 1k leather jacket and I would feel like an idiot, not that mature yet.
Then buy random patterned / picture tshirts, jackets, hoodies, hats etc when I see ones I like.
I deffinety agree with the traditional brands thing, either get something that will still be cool in 20 years like plain Lacost/Ralph Lauren or get it cheap. Most brands/fashion come and go so quick you will feel like a plonker 6 months later when it looks dated/becomes chavvy.
Or just buy cheap stuff from second hand or TKMaxx/Primark if you can be arsed rummaging.