Cigarette smoke irritates the lining of the nasal cavity and throat causing swelling and catarrah. If the nasal passages become congested it is difficult to breathe through your nose because the airflow is decreased. The likelihood of snoring increases as more cigarettes are smoked per day because the congestion increases with each cigarette. Even passive smoking can cause chronic inflammation of the nose and throat passages, thus increasing the risk of snoring. Children of parents who smoke are more likely to be affected by snoring than children of non smoking parents.
You may wish to try avoiding smoking for at least 4 hours before going to bed.
Hypnotherapy is ineffective as a treatment for snoring (because snoring is not a habit) but it can be effective with breaking a smoking habit.