A mannequin up left stuff

First thing to practice would be perspective. Draw boxes and cylinders in perspective. The figure is just boxes and cylinders that make up the mannequin. Once you can draw the boxes and cylinders comfortably, then move to the torso and pelvis boxes. Try to draw lines of action and then place a torso box and a pelvis boxes. Repeat until comfortable. Use pose references and just try to draw the torso box and the pelvis boxes to match the poses. This will give you the foundation needed to draw poses that are not stiff, that can flow with the line of action. I hope this helps and gives you some ideas on what to practice.

dont think about anatomical details yet, id say focus on construction and perspective first after that proportions of the figure.