Try blocking out the figure before you detail it. Concentrate on the things that would make your mech badass. smaller head and torso, bigger arms and legs (not too ridiculous of proportions). If you run out of room on the paper don't be afraid to chuck it and start it out smaller on the page. Try a more menacing pose or if your designing it, just do a basic stand up pose. Just make sure it's still imposing even though its just standing there. Shoulders back, chest pointing upwards, legs apart, wrists slightly bent in while in fists. Practice drawing hands.