When I was growing up, I had a rounder face until age finally did me a favor for once by helping the cause and narrowing it into more of an oval shape. Nonetheless, those with a fuller face structure like I formerly had often have a harder time slimming it down. Of course, you can suck in your cheeks and find cheekbones to dust with a darker contouring shade of blush or bronzer before applying with a lighter shade at the top of those bones to create more of a chiseled structure.
Another wonderful way is to get your highlighter and dust your cheekbones, forehead, and the bridge of your nose before you put on your foundation. By doing so, you will draw eyes to a better defined bone structure from the way light will fall on bones and the contours of your face.
I do hope you try this technique because all you have to loose is a bit more face!