Mix the eggs in slightly. Mix to incorporate thoroughly. Do not over mix the dough. The tips below will help you make a variety of cookies. When your cookie dough mixture is dry, add an egg yolk instead of water.
Water makes a dough tough.
The fat content of an egg yolk will keep the dough tender and its emulsifying action will help keep it moist after baking. When using a package mix, follow the directions on the package and if the cookies come out perfect continue to do so. However, since your kitchen environment is unique you may need to make changes in your mixing times, baking times or oven temperature. Directions are used as a starting place to doing things correctly and sometimes must be changed to make cookies the way you like them. Crumbly cookies may be caused by over mixing the batter.