Smudging is a energetic clearing practice found Native American traditions and in many cultures around the world. You can use smudging on yourself or on a space to clear out negative energies, this involves burning a stick of sage or other type of herb and moving it around the the corners of a room or around yourself.
To begin smudging you'll need a bound stick of herbs, white sage being by far the most common but you can also use desert sage, lavender, cedar, sweet grass or other types. You will also need a way to light the sage and a bowl for catching ash. Before you smudge it helps to set your intention of clearing yourself or a space of negative energies. Take a moment before you begin, take a deep breath, center yourself and put your intention on the ceremonial act of energetically clearing.
Begin by lighting your sage stick well so that it flames up a little and then when it begins to glow (a little like a fireplace) blow it out and you'll have a gentle glowing smokey stick. I tend not to use a lighter for this as it can get hot before you get it properly lit. To keep it going as you smudge just blow on the glowing center.
If you are smudging yourself move the smudge stick around your whole body, make sure to get your feet, hands! If you are doing it for a space move along the walls, into the corners and around the edges of doors or windows, after this I like to do a few swirls in the center of the room for completion. You can use your bowl (I prefer a small ceramic one or an abalone shell) to catch the ash as you move around or you can keep the sage in the bowl as you smudge. When you are done you can stub out your sage gently in the bowl to use again another time.
On an energetic level smudging cleanses the aura and spaces but an a physical level sage has been shown to clear up to 94% of airborne bacteria and acts as a powerful disinfectant. Sage releases negative ions when burned and helps to put people into a positive mood.
There is not a set time, day or amount you should do smudging, simply follow your intuition and how you feel if you are in need of a good cleansing! I would recommend to sage any new space before you move in to clear it of stuck or stagnant energies. If you have had a particularly rough day give yourself a good smudging and you should feel better afterwards as it clears out the negative energies that can attach to us on any given day.