Incremental. I’m no expert, but this is what has worked for me in the past.
If you want to “diet* and exercise” then I suggest not starting both simultaneously. Pick one and start that.
As with any big changes, start with some moderation. Don’t expect wholesale perfection right out of the gate. Then work your way up in frequency and intensity.
So, should you work on exercising or eating habits first?
I suggest starting with a moderate exercise program first. Why start with exercise? If you start exercising and get in the habit of it, you will start to feel good about yourself. You will feel better physically and mentally. You will have achieved something which gives you confidence to achieve even more.
Start slow, a few days a week, then build up the frequency and intensity of the workouts. By starting only a few days a week, if you miss a day here or there, you won’t write off exercise as a failure and quit. Start with a commitment to exercise 3 days per week. After a few weeks, add a 4th day, then 5, etc.
After a few weeks of exercise, you will start noticing that you are getting into better shape because your muscles feel better and you are more alert. Then you will hopefully come to realize that eating like crap and smoking is really holding you back on your fitness goals.
You will see that you are exercising regularly, but all that work you put into exercise is going to waste in large part because you are eating garbage food. Why are you pouring all that time and energy into exercise when your eating habits undermine all your exercise work? Here you are, exercising 4 times a week but all that junk food is preventing you from really making the most of your efforts. You will start to see that every time you exercise, instead of losing weight, all you are doing is trying to burn off all the crap you ate earlier in the day. You will realize that all your workout efforts are wasted, in large part, as long as you keep eating garbage. That realization will motivate you to start eating better.
Start with little things like refusing to eat the chips that come with your sandwich. Pick a healthier sandwich than the one you normally get. If you go to McDonald’s, get a grilled chicken sandwich instead of a Big Mac. Switch the late night snack or dessert to cottage cheese or a bowl of cereal. Stop eating dessert. Stop late night snacking. Control your portion sizes. Cut out fried foods. Make incremental change.
Start eating better a few times a week, then work your way up to eating better all the time. You have breakfast, lunch, and dinner 3 times per day, 7 days per week. That’s 21 meals per week. Start eating better as much as you can, but don’t expect to eat perfectly healthy food 21 times per week right away. Count how many crap meals you eat in a week then work on reducing that number each week.
When you start eating better, maybe you eat junk food 14 times per week. After a few weeks, perhaps you will eat junk food maybe only 7 times per week. Eventually, you get down to eating junk food maybe only 2 or 3 times per week. Eventually, maybe you limit yourself to eating junk food only once per weekend. When I was in my best shape, I allowed myself one meal per week, on a weekend only, when I could go hog wild and eat whatever the hell I wanted. This kept me from going crazy.
By starting exercise first, you will also hopefully come to realize that your ability to exercise is limited by the fact that you are smoking. I never smoked so I don’t know how it works. However, I would hope that, through exercise, you will start to see that your lung capacity is holding you back. Your muscles will tell you to keep going, but your lungs will want to quit. This will motivate you to stop smoking.
So, this is my domino theory, and it all starts with exercise.
*Change your long term eating habits