Perspective, expression, and pose practice.
I may color, I may not. :)

Originally, I had my left arm up and outstretched, however, I just couldn't pull off the "stretching" look. To me, I looked like I was extremely frustrated or super enthusiastically doing "YMCA" while sitting on the floor. While both are totally likely to happen, they weren't what I was aiming for. So, I moved my arm behind my head and I think it came out nicely!