It has to become a way of life, rather than a diet. You need to change your attitude to food.
We have been conditioned to eat loads of crap food that raises insulin levels which in turn has us craving more sugary food. I.E. McDonalds.
For me, higher protein, higher veg and lower crappy carb works.
Typical British diet:
Brekkie: Cereal
Biscuits as a snack
Lunch: Sandwich, crisps, choc bar, maybe a banana
Dinner: Spag bol, garlic bread.
This is really crap. It's just white flour and sugar.
Think of food as fuel and medicine for your body and you need to nourish it as best you can.
So, instead:
Porridge/eggs/yogurt/fruit/seeds for brekkie
Snack: apple and peanut butter, hard boiled egg and an orange
Lunch: big salad with chickpeas/lentils and lots of protein, so cheese, meat, fish. The fibre and protein will fill you up.
Dinner: Steak, salad, baked potato
For me, the key is eating natural, unprocessed foods. Lots of veg, soups, stews, salads.
It isn't necessary to have bread, potatoes, rice, pasta with every meal. We think it is, but it really isn't. You will survive, you will get through the day without white flour!
As a kid it was always 'finish your plate'. But leftovers are fine, you can take them for lunch!
Portion size makes a big difference. You do not need a massive amount of mash, two heaped tablespoons is enough! You need lots of veg, protein and fat to fill you up.
The key for me was cutting down on bread and pasta and eating ryvitas, fruit, porridge, eggs, yogurt instead for breakfast, and butternut squash and lentils instead of pasta for bulk.
You also need to actually find food that you like that isnt the usual crap.
So instead of spag bol, have red peppers stuffed with bolognaise with a spinach salad, or sweet potato wedges.
I've successfully lost 4 stone and kept it off for the last ten years.