In general, the present tense is used for habitual, regular, and/or consistent qualities or events. The present progressive is used for ongoing, unusual, and/or transitory qualities or events.
"I don't smoke" (= "I am not in the habit of smoking, either now or in the foreseeable future")
"I am not smoking" (= "Ordinarily I do smoke, but not at the present moment")
Using the present tense indicates your intention to continue a certain practice into the foreseeable future:
I used to smoke two packs a day, but I don't smoke now.
I used to live with my parents and do nothing all day, but then I moved out and now I work out five days a week.
Since I live on my own, I cook dinner for myself every night instead of going out to eat.
For activities that resume, which you use depends on what you want to say. The present tense indicates you feel it's a long-term change, while the present continuous suggests you feel it's a short-term change:
I heard you didn't smoke anymore, but now you do? (long-term change)
I know you quit smoking, so why are you smoking now? (short-term change)
I've become so lazy. I don't work out like I used to. (long-term change)
I used to cook for myself, but now I work such long hours I'm eating out almost every night. (short-term change)