Standing barefoot, try and grip the floor with your toes, spreading them out. Once you feel like you've got that down, try and lift all of your toes off of the ground a couple of times. If you master that, practice lifting your big toe while keeping your other toes on the ground and then the opposite, keep your big toe on the ground while lifting all of your other toes up.
This is all about learning how to maintain your stability in different weight-bearing scenarios. Standing barefoot, with your feet close together, try and bring your weight as far forward as you can while keeping hips/knees straight and feet flat on the ground. Then see how far you can lean back - a lot like trying to stand up on a train or metro.
THE SLIDING LUNGE
On a hard surface keep one foot on the ground, barefoot if possible, and put the other foot on a washcloth or just wear a sock. Put about 90% of your body weight on the foot that is on the ground, and with your other foot slide the opposite foot as far forward as you can while keeping most if not all of your weight on your foot that is staying still. Complete this again to the side and back as far as you can control. Then do the other side.