Well, it depends. First of all, we’re assuming you’re asking non-smokers. When I was a smoker, I actually preferred smokers, so that they didn’t complain about my own habit. Now that I’m not, I prefer non-smokers for the opposite reason.
But I would not say “never”. If she were a light smoker (my last gf was) and it did not stink too much, I’d accept it. My last gf for example would always smoke out in the balcony. Yes, her breath stank afterwards, but overall we had a good relationship so I didn’t mind.
Drugs (or even alcohol) are a different story altogether. Any type of addiction or obsession can affect your character and your behaviour, and therefore I’d be a lot more picky about such things. I’ve had a serious relationship with an alcoholic, and I don’t want to go through that again. No, I’d generally steer clear of people who do drugs on a regular basis, even if it was soft drugs. I might put up with the odd joint once a month or something, but that’s my limit.