I think like most things in life it becomes a habit and it helps that, when I get an idea in my head, I'm determined and persistent. The phone apps help immensely, 1. calorie counter and weight tracker and 2. step/distance counter and daily tracker (I keep these separate as otherwise App 1. would start adding burnt walking calories to my daily allowance) ! These can massively incentivise you and pull you back on track when you start veering off path (chocolate, ice-cream and hotel buffets) !
Initially 1,700 calories a day (compared to the 3,000+ needed to stay at my obese weight level). Now I'm at 2,000. A typical male of my height and weight needs about 2,500 a day to stay at a level weight. The hikes and walking (10kms a day x 4-5 times a week) bite off substantial calorie chunks to add the mild progress from a slightly lower calorie intake.