/ic/ - Artwork/Critique

So I was doing some sketches and noticed just how bad the form/proportions are in them. The models to the right are the correct proportions for reference. Can anyone give me some advice on something I'm doing wrong and how to correct course? I've gotten used to using 3d posing models as a crutch but more often than not the poses come out stiff and lifeless, and thats a pretty shitty practice I've been trying to quite anyway.

Also, this is a pretty scaled down image from when I was drawing, I'm not a regular here but I vaguely remember a general rule about image sizes not being too big. If this is too big or too small let me know.