Mix until combined. You want the dough to be formed into a ball and not sticky before removing from the bowl.
Then take out the dough and place on some wax paper. Knead with your hands. Keep kneading until it forms a dough-like consistency. If it's still too sticky add another tablespoon of cornstarch. Keep kneading until it is no longer sticky and is soft.
Sprinkle some glitter on (optional) and knead in.
Video
Notes
Note: if you find it is really sticky and not coming together, add another tablespoon of cornstarch and knead in.