Really useful info: HOW TO CLEAN, CLEANSE, CHARGE, ACTIVATE AND PROGRAM YOUR CRYSTAL – By Karen Ryan

“To prepare your crystal for healing, first clean the crystal physically of any mud, oils, sand or other debris. Then using a cleansing technique, be sure any negative energies are removed from the crystal so that you do not transfer residual energies onto yourself or your client. For maximum healing effects, charging crystals will ensure the crystal is ready electromagnetically and saturated with ultraviolet light which energizes each crystal. To “wake-up” your crystal, you may need to activate it into its role and mission.. And finally, program your crystal to direct the energy for a specific outcome or for support during a healing session.”

(I found another slightly different method on this site. Chose whichever suits you best.)

Also see Crystal Healing Tips – These are really easy. I especially love crystal dreaming and crystal baths.