Your altar is a representation of the microcosm and your relationship to these forces. Regularly cleansing and tending to this space is an important magical hygiene practice that will keep your life and your magical workings running more smoothly.
Choose a purifying or cleansing herb, such as sage, angelica, or rosemary, and place a few pinches in a bowl of spring water. Ask the spirit of the plant(s) to impart their powers of cleansing to the water, then leave the bowl in a sunny spot for a few hours. Strain out the plant material and pour the infused water into a spray bottle.
Mist your altar with the cleansing spray, visualizing all harmful or unwanted energy dissolving and returning to the cosmic cycle, leaving your sacred space fresh and revitalized.