Thighs: Heh. =P
Arms: Then try not to focus on making the arm curve. =P If you look at arms closely, there's more of a curve outward at the elbow, because of the bones there acting as a joint. That said, the curve isn't too obvious, it's more of a subtle curve, and is more pronounced on the inner part of the arm, from what I can see. =P
Waist: You should upload them eventually anyway; showing the progression is always a good thing, and as long as you pretty much explain that it's to help you practice and such, I doubt anyone would mind, and would like to see the evolution of your style. =P
Skirt: Makes sense. =P Something to consider is that you don't need to think too hard about it. I'm probably the worst person to explain this, since I can't for the life of me draw soemthing like a cel-shaded 3D model, but still. =P In your head, picture the scene as if it's a 3D scene like you'd see in, say X or Y. Easiest way to describe since it's done good at emulating the old style of battles with 3D, so it works for my example. For things like the skirt, think about how it would appear. In this case, it looks like it's sticking up in said 3D scene; if you want it to be more like how it would be in a 3D scene, an idea would be to drop the lines a little bit; gradually hiding the back a bit. Or at least not flipping it upward like that, since it looks like the wind caught it, and yeah. =P
That said, that part under Misu's chest really seemed like shading when I wasn't really concentrating on looking at the lines and such; might be something to keep in mind for shading. =) And also, shading will help with the 3D nature a lot too.
