Pre-treating stains is similar to the procedure used at home when you apply a stain remover to stains prior to washing them. The idea is to try to remove the stain or make its removal easier using chemicals. You can even help the process, especially if you catch the stain early! Simply apply water for wet stains (a stain that had water in it) and solvent for dry stains (a stain that has grease or oil in it). Then, gently tap and blot both sides of the fabric with a soft cloth so the stain "bleeds off" onto the cloth. Then, rinse the fabric, let it dry and your cleaner will do the rest.
If you don't know what to do when a stain happens, call your cleaner and ask him or her what to apply.