Great thread. I've really started to try and look a bit more polished in the last year, and I think I'm slowly learning.
I agree with a PP about sizing/fitting. I've always avoided petite ranges as I'm 5ft4, and the sites always say they're for up to 5ft3, but then nothing ever fitted right. I was buying size 6s to try and get clothes to sit in the right place. I've recently measured myself though, and actually I have a short body which is petite range, and I look a million times better for having dresses and tops that sit in the right place. The same with trousers - my legs are longer and not in proportion with my short body, so I've found I look better with slightly cropped trousers with flats, or an ankle boot/ankle strap to make my legs look a tad shorter. It turns out I'm actually a size 8/10 in a petite range.
Also agree about jewellery, I've stopped wearing jewellery apart from a very delicate bracelet, and again no necklaces because they don't sit right on my short torso. I really wish I'd known all this sooner, as I've started to take better care of myself all over now my clothes fit nicer, so I think it all intertwines.
I think I used to try too hard to attract attention maybe, and tried way too hard to be a bit edgy and cool, but it just doesn't suit me.