Thanks Cyangmou!
Yes, I've seen that tutorial, I think that I have even a copy.
Don't know why I did use white for that, probably I just wanted a clear contrast, And I wanted something bigger because I could't read well the figure small like it was.
 
Thanks again for that gif, it really answered many of my questions!

Thanks to all who answered!
Since I had the feeling that the figure wasn't ok and I needed to study some pose, I started to sketch some  figure. I worked with proportions too.

with some shadows


I left behind color and details  because I wanted to perfect the shape before.

I'll try with that exercise you suggested cyngmou, I still can't really see the right size/position of the parts, but I really think that with some practice I may be able to gasp it, also looking here and there I noticed that in most media there is the 7 1/2 ratio of the head, just knowing that table helped me to make a righter analysis of images and poses.

Thanks  Cyangmou!
I was searching a reference like that from ages, on Da there are many, but not as good as this.
Well, I tried to follow the guidelines, I couldn't stick with them too much, but it seems a lot better.
It's still rough.



PS: Cyangmou I really love your art! Your profile is awesome. I'm really glad that you replied to me.