When I was a teenager, I used to draw flat paddle hands or tuck them behind character's backs. It did wonders for me to just watch people and see what they did with their hands when they were sitting or standing. Much to my surprise, it turned out that it took more effort for people to hold their fingers perfectly flat. Resting fingers are naturally curved. Weird, right?
I just did a series in my comic breaking down skeletal anatomy, and geez... drawing the shoulder blades... those things are SUPER weird looking. It makes sense that they need to have spots for the muscles to anchor, but if you're not looking them up on the regular, it's easy to assume that they're just flat bones sitting on your back.