You want to have the correct sized duraball (antiburst) they are worth the extra $ as some serious injuries have happened with cheap swiss balls that burst when in use. Always place your hands directly under your shoulders open hands and activate lower traps i.e. draw shoulders down to back pocket and draw the lower abdominals gently in to protect back. Always breath – breath in on way back and out as you draw ball in. Do not raise butt up in air and do not sag back in middle – if you cannot easily be on top of ball with correct spine alignment and shoulders stabilised then decrease the load and have knees on ball.
Watch this video for all the above and correct demonstration by Josh from the Chek Institute. Happy Jack knifing peeps.