This is the Roman Rite for blessing incense. This is my personal choice for blessing it before use. It can be blessed in a large batch prior to any planned use or it can be incorperated into the ritual you are performing at the time. All you need in addition to the incense is holy water.
Lord God almighty, before whom the host of angels stands in awe, and renders you a spiritual service glowing with love, be pleased to look with favor on this creature, incense, to bless + and to hallow + it. May all weakness, all infirmity, and all assaults of the enemy, sensing its fragrance, flee and be kept far from your creature, man, that he, whom you redeemed by the precious blood of your Son, may never again suffer from the sting of the ancient serpent; through Christ our Lord.
It is then sprinkled with holy water.