You are mounted on opponent. You learn forward to move higher up on body, opponent pushes both arms straight up into your chest to push you up. As soon as he pushes, you fall forward on your hands, twist your hips out and move your left knee up by opponents head on right. Simultaneously, hold opponents arms near your body, and make sure your right let is out straight, pushing into opponents legs to pin him there. Next slide your right foot out straight and then wrap under opponents left armpit/shoulder area, squeezing in tight (like a pinch with both feet basically). At this point, slide your left foot out straight near your right foot. During this move you will sit back on the ground with both of the opponents arm. Holding the arm closest to your crotch against your body, lay back, bridge your hips slightly up and pull the arm down. Keep your feet down on the ground to control the opponent. From here the last step is to bridge hard enough to break the arm if absolutely necessary.

Note: In class we practice the form of moving to get into the position of the armbar, and not actually applying pressure to the arm. The point is for the good movement, and if your setup is good, applying pressure will come easily.