I've started trying to get in shape myself, I've managed to keep up the enthusiasm a lot better in the past year than in my previous attempts.
I started by changing my diet, I wanted something fast and easy to eat for work so I got things like fruit (bananas, peaches, apples, oranges specifically), pre-made salads and my grocery store also offers "snackers" which come with things like raw vegetables, humus, crackers, almonds, ext, that usually makes up my lunch.
My breakfast is one of those fruits above, plus some yogurt (the brand I can find with the lowest added sugar) mixed with fruit. I also sometimes eat cottage cheese, something with calcium in it so my doctor would stop complaining. I also sometimes have a smoothie for any given meal.
For drinks, I drink water, coconut water and sometimes tea or juice.
Also it's plus if I can find brands that are mostly real food and don't have sugar as three different names[footnote]stevia, evaporated cane juice, agave nectar, dextran, glucose, fructose, cane sugar[/footnote]
Since most of my time is spent at work, that's two meals I don't have to worry about five days a week, so I don't have to think much about what I'm going to eat and as long as I don't go overboard on snacks and dinner it works for me.
I also try to go to the gym, at first I didn't like the gym but it turns out, I was just going to a shitty gym. My sister showed me the one she goes to and another friend showed me how to use the equipment. I really like it and I try to go three times a week (or my doctor will yell at me).
(Gym routine is 15 minutes cardio, 45 minutes strength training, alternating between muscle groups[footnote]for example, one day back, chest and shoulders, next day core, butt, legs, it gives time for muscles to rest.[/footnote])
So I guess my advice would be... get a doctor to yell at you, or alternatively, find something that is healthy and works with your schedule.
Though if I were you, I'd focus on doing those things one at a time, if you didn't already plan. I don't think I could personally keep up with something like trying to quit smoking and getting into shape at the same time, that would take a lot of willpower.