Close lifetime smoker. Most are accurate to about 48 hours but the max is 96 hours. So the easiest thing is to stop for 4 days. If you don't have 4 days try to get at least 2 days and heavy brushing and flossing the day of the test and right before the test. Teeth, gums, cheek, tongue brush it all. Also, position the swab so it is in least amount of contact with surfaces.