There is no definitive answer to this question. People can, have and will successfully lose weight using a hundred different strategies as long as they satisfy the basic rules of energy balance. That said, here are three recommended strategies which don't rely on simply eating smaller portions of unhealthy food.
Drinking more water - Displaces calorie-heavy drinks like fruits juices, soft drinks, energy drinks, milkshakes and alcohol.
Eating more vegetables and fruits - These foods are high in nutrition and low in calories. Eating more of them leaves less room on the plate for energy dense starchy/fatty foods.
Restoring balance between fed/fasted states - Less frequent eating makes it harder to overeat.
Needless to say whatever habits you pursue consistency will play a vital role.