Cleansing is a pretty good thing to know how to do, whether it be used for preparing a spell, cleaning up after a spell, cleaning your tools, or getting rid of the funk after a bad day.
Smoke cleansing can be done with sage, bay leaves, or any type of incense. You waft the smoke over yourself or your space. Be careful while setting fire to those herbs though.
Water cleansing can be done by making a spray out of herbs like lavender and mint, its pretty safe and you should spray it all around the room or on yourself. Be careful though as water irrigates some crystals.
And the elements/natural world. The wind, the moon, the sun and many other things can act to cleanse as well.