My idea for a next step would be to advance that sphere shape you use to represent the chest area towards a flattened egg shape, that is closer to the actual anatomy of the chest. You will have to reduce the distance between hip and chest quite a bit, to make that work.
In the short exercise you always use quite a lot of lines to represent a single sphere. If you manage to draw fewer lines with more control the result will be clearer. Maybe spend some warm-up time just on practicing circles free-hand.
