Correction: The BEST AMAZING FUN BEAUTIFUL COOKIES party.
Step 1: Make the dough in advance.
Mix it a day or two before and let it hang out in the fridge for 24-48 hours.
Make a couple different varieties of dough.
Label them so you know which is which.
Here are some good dough recipes you can trust:
Martha Stewart's Basic Sugar Cookie Dough
Smitten Kitchen's Brownie Rollout Cookie Dough
Bon Appetit's Gingerbread Cookie Dough
Good Housekeeping's Lemon Sugar Cookie Dough
Martha Stewart's Cinnamon-Sugar Cookie Dough