I went on Nutrisystem for a month as I needed a "reset." Our kitchen counters were topped with snacks and candy, and I had fallen into the habit of mindlessly snacking every evening. Plus, I like to eat! :) At my heaviest I was 254 lbs - I'm 40 years old and 6' 2".
Nutrisystem (or any other "crash" type of diet) is painful. You crave food. But what's going on during this time is your body is getting over its sugar addiction, and learning to require less food.
When that period was over, I went to a diet of approx. 2,000 calories a day. 500 calories in the morning, 500-700 calories at lunch, same for dinner. No more sweets, except for a treat on Friday. No more snacking - after dinner I'm done eating. If I'm truly ravenous later in the evening I get an apple.
That's the discipline and habit part. Next is the mental, because it's easy to backslide. Plus, our own bodies may be fighting to regain the weight! https://www.nytimes.com/2016/05/02/health/biggest-loser-weig...
This is where I have to look at the opportunities to overeat and say no, every time, but ALSO to ask myself "what particular need, or hole, is this trying to fill?" The way I figure, the chronic overeating was me trying to fill a hole in my soul, so to speak, to fix something broken in my psyche by engaging in indulgent behaviors that feel good at the time. But, as future self will always tell you after a night of hard drinking, "now I feel worse, thanks jerkwad!"
So, basically, you gotta do the mental work as well. Figure out your hole - what does the food do for you that life does not?
Finally, exercise! When I first started I was "running" a little under 2 miles. Really, it was running a few blocks, then walking half a block, then repeat. I decided to go on a hiking trip with some friends in July, and figured I needed to be running straight for at least 4 miles by then to be in shape. To date I'm up to a little over a 5k, no walking. I got a bike, and I'm trying to get in at least 15 miles a week. Nothing crazy. Lastly, if you're strapped for time like I am with a wife and kid at home, the 7 minute workout is great for busting out a quick workout with nothing more than a chair and a place to do some calisthenics. It's HIIT, and helps with flexibility, strength training, and cardio - plus it's only 7 minutes.
For me, I'm just going for getting in some type of exercise at least 4-5 days a week. Once again, the mental plays a part here, because when you get home from work, exercise is often the last thing you want to do. I've noticed though, that as I get into better shape, it's the first step, or jumping jack, that's the hardest - after that I actually start to enjoy it. :)
Currently: 231 lbs. (and still going - I look for opportunities to eat less, instead of more. I want to go about 20 lbs more)
Disclaimer: obviously this is my experience, and won't work for everyone. But, I do believe that it's the attention to how much is going into your body, doing the mental work, and exercising that will make a difference for anyone.