like everyone said, balance it. if you have a cheese plate, this may help tho:
put a pencil under your camera in the direction of the lens and try to roughly balance it, then turn it perpendicular and do the same. where these two lines intersect is the center of gravity of your camera, and you should put this point as close to the center of the shaft as possible. Other than that, I think some people like to use a shorter drop time, and adding weight on top never hurts (from a physics perspective, though your forearm may disagree haha)