Put on one ballet shoe, leaving its back elastic bands out and accessible. Learning how tight your ballet slippers should be is essential, and it can be done only if the slippers are on your feet, which is easier if you deal with only one shoe at a time.
Pull the shoe's elastic bands over your foot. Two elastic bands are attached to the shoe at one end. Cross them over your foot to the other side. Ensure they don't twist anywhere along the line. The elastic bands should be in line with the seam on the side of the shoe. Pull the elastic bands tight, but not so tight that you feel pain.
Mark where the elastic bands and the top of the shoe meet. This is how you'll know where to sew the elastic. Release the elastic bands, and remove the shoe.
Sew the elastic where you marked, inside the shoe just beneath the top seam but still in line with the side seam. Don't sew into the seam on the top because that will prevent you from tightening the other elastic bands in the shoe. Trim excess elastic.
Repeat the procedure for the other ballet shoe.
Put on one ballet shoe. The front of the shoe should have two elastic bands that run around the shoe's opening. Tightening them tightens the shoe around your heel and ankle. The process of sewing the elastic bands is easier when done one shoe at a time.
Tighten the elastic bands just enough so the shoe is snug to your foot. If you overtighten these elastic bands, then they shoe will press into the back of your foot and cause discomfort.
Tie the elastic bands into a bow. Make the bow secure because you won't untie it often. Secure the bow to the inside of the shoe using masking tape. That task may be easier if you turn the shoe inside out first.
Repeat the procedure for the other ballet shoe.