Figure Study 1

I will pick out the main spots which are off, but honestly don't look back too often on these and just keep cranking them out.
The main things are the arms and head are much larger in proportion to the torso and legs. Her legs appear shorter amd oddly shaped because the shading where skirt curves over her knee is much lower down than where it should be.

I'd suggest nude models first...drapery makes things much much harder. I'd also suggest starting with quick gesture sketches (30s to a few mins each max), just thinking about action and volumes, to capture the essence of the figure. These will really help you nail down proportion and they are quick and fun to do.