Open your guard and swing your legs out. Your hips need to be loose and come out from under them; staying tight will just make the sweep harder. Rotate on your upper back.
Your right leg swings out to take them off balance, then you lift them with your left leg, then lift their knee, and all of this while pulling on the choke.
From this angle, you can see how he is using his legs and his grip on the knee to sweep me. Also notice how he has trapped my arm across his chest so I can't free it.
Come on top to finish the sweep. You can't see from this angle, but he has folded his right leg before I could land on it, as in the basic pendulum sweep.
Bring your left foot up and fold it towards their head. Slide your right knee up by their head.
Throw your right leg over their shoulder and trap their arm with your legs. Finish by grabbing the near knee and falling back, arching your back and pulling with your arm.
Enjoy.