In high school, I was in drama. I used to act until...
We were doing a production of I Never Saw Another Butterfly which was a very sad story based on the reality of children in the concentration camp Terezin in WWII. I was playing one of the children and did my own makeup. After seeing how I did my makeup, they promptly had me do all the other children's makeup the same way. Ever since then, I was put on the makeup crew.
Back in the 80's I remembered reading an article in Smash Hits about how Boy George used to put dark grey eyeshadow under his chin to try to hide his developing double chin.
Dark colours minimize.
I got some dark grey eyeshadow and put that into the hollows of my cheeks. You would also put it on the sides of your nose to make it look narrower and under your eyes for a sunken look there. For a more skeletal effect, you can even put just a TOUCH right at the "cleft" of your chin. Even if you don't have a cleft, it will give you one and give you a more skull-like look. You can also rub a bit into your temples above the brow bone. Look at a picture of a skull and blend the dark eyeshadow into all the places where it looks black.
You can also try putting a lighter coloured strip down the middle of your nose and onto your cheekbones to make them pop out a little more.