make your own food, use lots of vegetables and meat just to season it. eat salads but make your own, use fruits in your salads, use very little dressing. I like to drizzle a little bit of olive oil, chili powder and lemon.
you want something sweet, use a food dehydrator for fruits, heck make your own beef jerky too.
make it annoying and stupid to smoke and drink. I hate warm beer, so I put only 2 beers in a wine fridge, takes a couple of hours to get them cold enough. my cigarette are on top shelf of the cabinet, i have to get a step ladder from the office, to reach them and i only get 1. I'm down to smoking 3 or 4 cigarette instead of a pack a day. it's a big deal for me to climb the 4 steps so I use that as a way to stop.
I do engage in the occasional greasy burrito or pizza. if i feel like eating fried chicken I only make 4 pieces, instead of the 10 to 15 before.
basically, change at a pace you feel comfortable.
semp