Denim rocks! That's all there is to it. Denim is a wardrobe staple, and all women should have 3 pairs minimum.
Casual style for flats
Dark wash bootcut to wear with boots and heels
Funky, stylish denim fit--here are trouser jeans, or you could pick skinny, high waisted, or embellished styles
Denim fit is most important, though, and allow me to share a secret with you: http://www.zafu.com/. If you haven't already heard, this free website asks a few short questions then outputs dozens of denim styles and brands based on your body type. Think of all the time you can save in the stores thanks to this great tool!
Live in color!