In short:
Eat less, but better.
Don't snack.
Do not have your personal 'kryptonite' food/s in the house.
Move more. Do anything, anything at all, just move.
My personal story: I've been obese and I've been a healthy weight. But mostly I've spent my adult life in between, as an overweight, slightly portly, if still curvy, woman. I've rarely managed to maintain a healthy weight for more than a year at a time. However, in terms of the principles I've learned through the past decade it goes something like this when I'm slim(ish!):
I have no gears, no brakes, no natural mental stopping point - I am either on point, or I'm not. And when I'm not, I mean I'm really not! For example, I cannot snack in a controlled manner. I just can't. It is the highway to hell for me. Therefore I do best when I commit to a fairly samey eating plan, because it removes the element of too much choice. So my breakfast and lunch are almost always the same, six or even seven days a week. I love to cook though, so I satisfy that creative culinary urge through our evening meals.
I am a phenomenal emotional eater. Food has been my solace, my reward, my joy, my guilt, my self punishment even, for my entire adult life. And in combination with the above lack of self discipline, I simply cannot have snack/treat/'bad' etc foods in the house, because the urge to eat when I'm in any kind of emotional state is overwhelming. Utterly overwhelming.
Excess carbs make me feel like shit, emotionally and physically. Higher protein/lower carb eating has been an absolute revelation for me. I don't do low carb by any definition of the term, but I do try and avoid processed or 'simple' carbs & foods - cakes, sweets, biscuits etc. and concentrate on complex wholegrain and natural carbs (veg) wherever possible. I'll happily eat limited frequency and controlled size portions of wholemeal pasta and bread for example, but I avoid white rice, bread, and puddings. I try to eat more veg than fruit.
I exercise more. Losing weight goes hand in hand with improving my health for me, so I've usually always increased my exercise at the same time as I've reframed my eating. I can lose weight easily through diet alone but increased exercise makes the momentum much easier to maintain.
Ultimately I believe that naturally slim people who have never been overweight have a different natural mindset. It just is. Those of use who have been overweight tend to struggle more to maintain - it's a conciousness that the naturally slim don't seem to need.