Stand facing a mirror with your heels pressed together forming an outstretched "V" in first position. Hold onto a ballet barre if necessary for balance.
Bend your knees into a demi-plie, or a slight bend, with your knees pointing out over the toes and your back straight.
Raise your heels off the ground in demi-pointe, keeping your knees bent. Press your arches out towards the front of your foot as you do so.
Straighten your knees and raise to full releve. If you are wearing pointe shoes you should now be on full pointe. Continue pressing your arches towards the front of your foot.
Return to your starting position and repeat the process several times. Continue practicing and strengthening your arches by repeating the exercise in each of the five positions as well.