Put an apple under your chin!
This is possibly the oldest form of postural awareness technique in the west.
So, put an apple under your chin, it's experiential, meaning you have to do it, to feel it, to appreciate it.
Obviously the apple could be an orange, or a tennis ball, a baseball, not a rugby ball and not a coconut. Once the apple is dropped, because you will drop it, its utility is somewhat reduced.
I've got a training baseball, soft yet firm, but the classic is an apple, and there are many different types of apples of all different sizes, this being the principle of finding something that's adapted to you and your under-chin space and movement. A dog toy maybe?
Once the "apple" is under your chin keep it there, this is your first postural awareness exercise that puts your upper spine in a "nice" position.
Secondly, try and open your mouth gently, don't drop the "apple", notice how you're suddenly doing a movement which you do all day every day but differently.
Thirdly, look around, don't drop the "apple", try looking at the floor, ceiling, walls, tv, pc/mac, move around sit down, stand up, crouch down bend over and lie down. Well done if you got through all that without a bruised apple.
Finally, eat the apple if you can, you've just completed one of the oldest posture and movement exercises in the west, probably!
p.s. if too easy, put a book on your head as well.