To obtain the most reliable result possible, do not eat, drink, smoke, or brush your teeth for an hour before taking the sample. It is also important to remove all make-up from your lips.
Massaging the cheeks previously means you will obtain the epithelial cells shed from the inside of your mouth. Then introduce the swab or cotton bud in your mouth and rub energetically against the inside of your cheek for one minute.
Try not to contaminate the sample once extracted, making sure the swab doesn’t touch anything before putting it inside the container. See explanatory video: