This has been interesting, and I have read most of it. For me, and I'm probably 30 years older than many here, it's all true and none of it is a fixed rule.
Scrupulously clean hair, nails, teeth are rudimentary; we all do that. It helps enormously to have naturally good, moisturised, exfoliated skin, but aiming for a great natural complexion should be rule one. Posture really alters how you view yourself, and how people see you. The dancer's rule; think about the thread pulling you upward from the top of your skull and let the rest of your body follow the natural alignment that follows it.
After that, in my mind, it comes down to personal aesthetic preference. Personally it's a line midway between boho and classic. So I wear sheer blouses, but as I'm over 60, not over naked skin. I will pile on textures in winter, with a colour theme.
I buy basics, spend decent chips on them (great jeans as I wear them six days out of seven; a beautifully fitting down jacket (neutral or contrasty to please yourself, but a colour that works with most of your wardrobe. Current version is navy, but the alternative would probably be orange or olive. Occasion wear is always bought in sales: I always spend more on the things I wear every day. T shirts and jumpers come from Uniqlo and are replaced when they look tired.
The fashion bit comes in the accessories and styling. If your taste is fairly classic, spend the money on shoes and bags,maybe jewellery; if it's not, then buy the most outrageously high fashion things you love and be prepared not to fall in love with anything to recycle your less successful purchases for more than a season. I decided a long time ago that accessories were to be lent to friends (the ones who would return them, dry-cleaned) because those things would be versatile and fit for much longer than a dress. One is never too fat for the right scarf, but having it or being able to borrow it, often salvages a cheap frock for a posh event. But real every day life, that is where to spend the money. If you are going to wear it, or similar, for 300/365, why would you not put most of your clothes budget there? Most of the rest is putting in the grooming time, which is not to be under-estimated.