One thing that might help is to eliminate the allure of smoking and/or drinking. Between 6 and 13 my mom occasionally told me that if I ever wanted to drink or smoke, that I should tell her and she would buy the alcohol or cigarettes and we could sit in the back yard while I smoke and drank. To this day I have never smoked and only get drunk twice. I also get irritated when people list the reasons why I should go to an event and one of them is cheap alcohol.
When I was about five my family was sitting watching Ed Sullivan.I was sitting next to my Dad and I asked him if I could puff his cigarette.To my surprise he let me...I took one puff and couldn't stop coughing for about 10 minutes.My Mom was livid."Why did you do that?",she said.But whether my folks realized it or not my Dad had done me a huge favor.My experience caused me to form such a negative opinion of cigarettes that I never smoked.
Both my folks died of smoking related illnesses,but I won't.
I really do buy the idea of ‘additive personality’ (which I am not, generally). Although had tried both smoking and drinking by 16 or so, they didn’t stick. Even now I will buy an 18-pack of beer and it will take me a year or so to get through it. The chemical substance matters a lot, though. I think I would get addicted to oxycodone or another opiate within a week or two, judging by the few pills I’ve been described.