You're off to a fantastic start! Quick gestures about 30 seconds and under usually aren't very detailed or clear aside from the general idea of the pose, so you nailed that. I do however think you should try to include the whole body anyway!
Also, I think it would be helpful to use actual paper instead of the back cardboard of a sketchbook; I find for doing lots of quick gestures, you should use a big piece of cheaper paper, and for longer gestures, use smaller, high quality paper. I like to use sheets of copy or animation paper for my gestures 1 minute and under, and cardstock or mixed media paper for anything that's 5 minutes or more.
1
