Graham cracker and crushed cookie types of crusts are usually pre-baked. Always check your recipe to make sure whether the crust is pre-baked or not. When using your mixer, make sure that you use the beaters designed for pastry mixing. Do not over mix the dough. When using your blender, make sure that you do not over mix the dough.
Blenders mix the dough very quickly.
Make sure that all your utensils are clean. Use chilled shortening and ice cold water in the mix. These ingredients should be blended well. Water and salt will cause the pastry to be tough, so dissolve the salt in the ice water and add it last. Blend the dough only until the mix is not wet and sticky feeling.