Cleansing and purifying your crystals/stones regularly is great idea as some of them may absorb negative energy or vibrations from you or their environment. Frequent and regular cleansing will ensure that they have the highest vibration possible and remain effective. Please treat your crystals as tools that support your healing practice, but be sure to exercise caution when using crystal as a method of natural healing - use your own discretion.
Smudging is the ancient practice of using smoke to purify your space, aura, and crystals. White sage and Palo Santo wood are typical smudging materials, which can be readily purchased online.
To smudge, light the leaf tips of a sage bundle or one end of a Palo Santo wood stick. Surround your crystals with the smoke for a minute or two.
Direct sunlight is one of the most purifying elements. Allow your crystals to be exposed to direct sunlight for a few minutes to cleanse them. An easy way of doing this is to place your crystals on a windowsill.
Crystals can be re-charged under moonlight to reinvigorate them and raise their vibrations. The energy of the moon is the brightest and most powerful during a full moon. You can also place your crystals on a windowsill to do this.