1. The angle here is not completely clear. I assume you're drawing from a side view, and to that I say the shoulder should be moved up to obscure part of the body. Right now, your character probably has arms coming out of his, like.... shoulder blades. The body is a 3D object, so arms will always be coming out of the sides.
2. Humans have an s-shaped spine (outlined in blue). It means the back curve s into... sort of an s shape?. How much will depend on the character's body type, but overall the body is probably not a box unless the character is REAL cartoony.
See? Check out this stock photo guy!
one shoulder? Check!
s-shaped spine? Check!
Anyway, my number 1 tip? Use a reference photo. Heck, I googled "Person from the side" while I was drawing this! Even breaking those down into basic shapes can really help you!
