You can slim the appearance of your nose by using a darker concealer down the sides and a lighter concealer (or highlighter) down the middle of the nose. You must blend it all well or it'll look very strange.
To contour your cheekbones, look down into a mirror and find the natural shape of them, and with a blusher brush, apply bronzer or nude blush into the hollow beneath the bone. Highlight above it.
Hope thats some help...