Often the great elicitors of the lean back are knees which either lock when the heel strikes or lock and point toward each other. By keeping the knees soft and slightly open, you elicit the optimal weight forward position. It is the same combination that stabilizes your spine during walking. Taking a long inhale through the nose should expand your rib-cage sideways. Your ribs should move toward your inner arms.
Many people breathe up into their chests or out into their bellies.
Both of these elicit the lean back. At the end of a long proper exhale, you should experience a lower abdominal contraction, which is another crucial element to keeping your weight forward. The exhale will also make it easier to lift your leg in a perfectly controlled manner. It only means that you feel the weight of your whole body toward the front of you instead of your rear. It is the glue that stabilizes your spine during walking and strengthens with every step you take, if you stay forward.