I will say what worked for me ( lost 30 Kgs ( 66 Lbs ) in ~6 months ) sorted by what I think it is easier and more effective:
1. Eat slowly, as slowly as you can, the feeling of being full takes a while to reach your brain ( I know this is not the scientific correct definition but gives the idea ), the slower you eat the less you eat.
2. Drink a lot, something I noticed is that sometimes I want to eat something but the reality is that I want to drink and I'm just eating to get the liquids out of the food, when you want to eat first drink a glass of water and wait 1 minute to see if you still want to eat.
3. Brush your teeth 5 minutes after you eat anything, I myself find washing my teeth a chore and I want to do as less as possible, brushing my teeth after lunch stops me from eating snacks after lunch because I don't want to dirty my teeth and wash them again.
4. Have a food journal, use an app to log everything you eat, before you eat it. It is important that is before because in this way you know how many calories you are going to eat, and sometimes that number is higher than what you expected, at least on me this usually has the effect that I choose to eat less of what I was going to eat or I will eat something else entirely.
5. Eat breakfast as late as you can, and dinner as early as you can. This is called intermittent fasting and works, but it requires quite a willpower.
6. This one is the one I find the hardest but also the most effective: Limit the amount of sweets you eat, I know it is hard as hell and when you see a sweet you already start salivating ( or at least I do ), but say to yourself: "today I will eat maximum 250kcal of sweets ( that is usually 1 croissant max )" or if you are more advanced you can swap today for "this week"
7. This one doesn't really apply to me because in my country we have the culture of cooking, but from what I heard around it helps in countries where cooking at home is uncommon: Cook your food from scratch, don't buy a ready meal, cook it yourself, in this way you have full control of what goes in that meal and you know what goes in it, it will save you from eating unnecessary sugars and conservants.
edit: formatting