Sage smudging is an ancient ritual used to clear away any negative energy. It is also a great tool to use to cleanse your crystals before and after use.
 
TIPS:
Light the end of the sage stick and allow it to burn a little and then blow out any flames, there should be a steady stream of smoke flowing. 
Sage should never be lit and left unattended
Keep out of reach from children
Direct the smoke with either a hand fan or simply wave the sage stick in the area that requires cleansing (always a good idea to keep a small plate or bowl underneath as you go to catch any bits of the stick that may fall)
If you are cleansing the house/or room, open all the windows once you have finished to flush out any negative energy
When you are finished always best to run the end of the stick under cool water to put out any burning.  Leave somewhere safe to dry until the next use