i'm currently using 24mg when I need a heavier dose and 16mg the rest of the time. I was a two pack a day chain-smoker. But, that being said, everyone is different and has different tolerances, etc. For example, when I tried the patch i was smoking while wearing the patch. *hides face*
It will take some experimentation to find what works for you. And, if you find you have ended up buying juice that's too low, keep it on hand for days when you only need a light dose. If end up with buying juice that's too strong, offer it up in the classifieds/swaps area.