When contouring your cheekbones with a powder, use a slightly pointed brush or a dense brush like the MAC 109 and start from next to the ear going down the cheekbone. Go in small circular motions, avoiding a straight line down your face. The circular motions, will blend the contour powder in to look like an actual shadow and give you definition rather than just a stripe!
Also, less is more, start with a little product and gradually add more if needed. Always better than using too much and then struggling to blend it out...
~ Shez ~