For hotels, I usually bring a travel candle holder (metal, holds a tealight candle and has a lid - sold at Pottery Barn and such). Then I can light a nicely scented candle beside my bed and freshen the air. But I assume the use of candles is frowned on for cruise ships.
I hope our room isn't booked the weeks prior to our trip by heavy smokers. It is a RCI Explorer of the Seas Promendade View room, which means there will not be an balcony or window we can leave open to air out if previous smoke is a problem. I have asthma, so this could be a big concern if the room is very bad, and we really hadn't expected a problem like this when we booked three Promenade rooms.
Jeesh, I hate smoking - I wish the government would ban it everywhere, and I mean everywhere, except one's own home and one's own car, period!!! It shouldn't be legal to impose one's cancer-causing, allergy-triggering, asthma-attack inducing, dirty, foul-smelling personal addictive habit onto other people.