A few thoughts:
1). Don't take a big step back -- step back under the shadow of your backside -- if you want to take a bigger step, then adopt a Lindy style posture
2). Don't lower your foot quickly when you step back -- keep most of the weight on the ball of the foot -- almost like a *proper* back rock
3). Take your hand back behind you before you step back, as in Savoy style Lindy.
SpinDr.