Hmmm FWIW! As a minimum and on a budget...
Good basics... Jeans, chinos, underwear, a few nice cardigans, crisp t-shirts, a few good belts. Don't have to be expensive
Never mix base colors... So pick one of grey/black/navy/brown
If trousers have belt loops, wear a belt
Never have visible underwear/bulges/straining buttons, pulls, stains, bobbles
Wear either lose top / fitted bottoms or vice versa but not both
Don't show too many of toes / knees / elbows / shoulders / cleavage at once
Wear shoes you can walk comfortably all day in
Wear the best watch you can afford
Avoid all visible labels/branding
'Do' something with your hair... Straighten, flick, smart ponytail, braid, front clipped up. No curtains or mum buns
Wear a bit of makeup
Wear some jewellery. But not too much.
Wear one interesting thing with each outfit... Bright shoes, interesting scarf, nice bracelet
If you have to spend money on anything, spend it on shoes
Assemble your entire outfit before you put it on
If it feels uncomfortable when you put it on, change it
Carry one bag if you can.
Wear layers... Thin vests and cardigans are great...