Frankincense resin works best for me. We have a charcoal burner. I go room to room. I get it in bulk from different places, but you used to be able to get it from Perfect Potion, I also have got it from Esoteric Bookshop (which has an online store) and Spellbox in Royal arcade. I prefer charcoal burning and herbs/resins as oppose to smudge sticks, as they've never done much for me.