Woodchoppers are great full-body moves. Do let you feet rotate to protect your knees from over-twisting. Do start with no weight, or use no-weight for a warm up, then add a medicine ball or dumbell/sandbag/whatever you have. These are also nice with a broom handle, to get you thinking about drawing a big arc with your arms, through the sky. Do use your legs; after you are warmed up, think about exploding off the front leg to bring your body back up. Do go for smooth and steady movement.