Besides the drawing advise you already got, I wanted to talk about your values. The figure overall is too light, especially the shadows. You also made the reflected light too light causing the figure to look like it is cut out and pasted onto the background. I did a quick paint over to show you what I mean, I hope it helps :)

Beautiful work @W.I.M.U! Awesome job for a first charcoal drawing attempt. You have a great value range. One thing I noticed that could help you bring more rhythm to your drawing is to emphasize the relationship of the tilt of her hips against her ribcage. It's pretty subtle in the reference image, but there is a bit of stretching and pinching happening between those two structural landmarks. Using your knowledge of anatomy, you can push those relationships to make this fairly static pose more dynamic.