Generally I make my cookies right before I am going to use them. They taste best when they are at their freshest. But if you do want to store them, here is what I suggest.
Decorated cookies should be completely dry before storing. I use the Ball Pin Test to be sure. Poke a pin onto the surface of the cookie—if it doesn’t puncture the surface, the cookie is thoroughly dry. Once they are dry, you can store decorated cookies at room temperature between sheets of waxed paper in an airtight container for 2 weeks or in the refrigerator for up to a month.
To freeze cookies, which keeps them freshest, wrap each one in a resealable plastic bag or tied cellophane bag. Place in a freezer-safe container and freeze for up to 3 months. To thaw, leave the container out at room temperature. Because the cookies are in bags, any condensation that takes place will happen on the bag and not the cookie.