Avoid buying materials that are too cheap as they are usually not flattering or will not last. You can see some characteristics of materials here. Best to buy only the clothes that you love and that have a chance of lasting.
Don’t mix a fitted skirt or slacks with a tight top. Aim to have either a fitted skirt with a loser top or the other way around. See also my suggestions on the best ways to wear leggings over 40.
Nothing is more vital than dressing in a manner in which pleases and exemplifies you. If you know your style and understand your body you can break any of the guidelines or add items from the ‘don’t list’ as you please. My find your style obstacle will help with that.