Don't smoke too much and try not to smoke and drink at the same time. Also, 10 mins of running / cigarette smoked. And last, don't drink more than 3 days out of 7. Your liver will say thanks.

PS. also, don't smoke while working, even if you can. I know it's tempting and very pleasant but that's exactly how you cross the 1 pack/day limit.

PS 2. in case it's not clear, by smoking I mean cigarettes. Weed is another subject. Personally, I try to keep it an unusual exceptional treat, something like once a month.