Hello Sanjanart and I hope you are well. I think determining a Line of Action would be helpful for your gestures. One way to find it is to find which parts of the body are bearing weight and loosely draw a line through them to the head or another convenient body part. As for the chest area or ribcage try thinking of it as a bell or an egg shape. You could even draw it as a boxy shape. Sometimes it tilts in the opposite direction of the pelvis like in your first image. Look up “Contrapposto” for a better idea. As for curves and angles try to have them follow or emphasize the forms of the figure you are drawing. I think you would find the book, Force: Dynamic Life Drawing for Animators by Mike Matessi, very helpful for this and for gestures in general. Some knowledge in anatomy also always helps. I’ll try to post a drawing that will hopefully help you too. Best of luck and keep up the good work!