In a facial exercises book I have, there is a "Cheek Lift". It says Imagine a dot on your upper and lower lips. Open your mouth and pull the dots away from each other and form long oval shape with your mouth. Place index finger on chin for resistance. Look towards top of your head and squint up with lower eyelids. Raise your cheeks up by forcing a smile with upper lip. Push smile under the cheeks and hold for count of 30. Press lips together and blow. Do this twice a day.
you can have botox, or some poison or another injected into your cheeks. it will plump them up more in the area you want which may give them more definition
Now you have had a couple of sensible answers, can I jokingly suggest an alternative of having your shoulders lowered! Sorry, it's been that kind of day lol