The initial dosage is individualized and determined by you and your doctor. For many, the best effect is achieved by frequent, continuous puffing for 20 minutes - about the how long one cartridge will last. A cartridge delivers about 4 mg of nicotine, though only 2 mg (the equivalent of about 2 cigarettes) are actually absorbed. After placing the cartridge into your mouth, use either shallow or deep breaths to bring the nicotine into the back of your throat.
For more information see: http://www.nlm.nih.gov/medlineplus/druginfo/meds/a606021.html