Sitting on a firm chair: sit up tall with your back away from the back of the chair, place your foot on a ball and roll the ball under the inside of the sole of your foot, then the outside of your foot and finally the middle of your foot. Pay attention to what you are doing and what it feels like for your foot. You can do this using any type of toe separator or without anything between your toes.
Sitting on a firm chair: put your heel on the ground and the ball of your foot onto the ball so it supports the front of your foot, flex your toes down then pull them up into extension, spreading your toes apart. As you pull your toes up make sure the ball of your foot stays firmly on the ball. It may help to push the ball of your foot onto the ball as you pull your toes up.
Standing: try to feel where the weight is on your feet, is it more on your heels? more on the balls of your feet? Once you have a sense of where your weight is on your feet, lift your toes up so you displace your weight into your heels, then take your weight forward into the balls of your feet (without lifting your heels off the ground) and repeat two or three times. Now try to find the middle of your feet so you have weight equally on both your heels and the balls of your feet. Make sure your toes are relaxed. With your toes relaxed imagine growing roots into the ground from your heels and all five metatarsal heads in the balls of your feet. Feel how grounded that makes your feet. Now, where does your weight feel like it is in your feet? Can your toes relax more than when you started?
Before you do any exercise try to find the center of your feet so you are driving the muscle activity to do the exercise from solid yet adaptable, active, and stable feet.