Try and be mindful on your “normal” days. Normal for a lot of people is eating way too much. Work out your TDEE amount and count calories to start with to compare what you think is normal to what your TDEE amount is. They may be very different.

Avoid sugar at all costs and simple carbs like bread, pasta, rice, potatoes pizza etc. Avoid fruit juice like the plague. Whole fruit is OK but have it in moderation. Fruit juice, no way. Sugared drinks and even artificially sweetened drinks are a no go zone. They spike your blood glucose which means storing what you eat as fat.

Good luck, it works if you give it a genuine try.