Keep it simple. Usually chinos, jeans or leggings with a plain fitted vest or T shirt, longer with the leggings to give a sleek look.
One piece of jewellery.
A good handbag. A selection of good jackets, Chanel is my go to, but also Farhi/Hobbs - mine are vintage now, had them so long.
Co-ordinate colours, only ever one pattern at a time but mostly plain.
Flat or very low heels, only comfortable tried and tested footwear, hobbling or staggering is not a good look.
With skirts, check the length of the coat you are going to wear, bag lady is also not a good look.
Cardigans rather than sweaters, easy to wear open over a top or buttoned as a jumper. Easy to slip off when hot.
Always check back view, so many people either don't bother, don't think of it or don't have a mirror.
I also like a boho look when wearing skirts or dresses but still simple.
Layers always.