your body will burn more fat in a fasted state. start there
that is the 1 non broscience tip i can give you
the key is though not gaining it back. our bodies are either going to store or burn fat. so it starts with how, what, and how often you eat. you won't outrun a bad diet so don't even bother.. so don't think you can burn 1000 calories doing cardio, then go to chikfila and eat 800 calories and lose weight.. nope, doesn't work like that.. your body will STILL store fat after that meal because of how it is made and what is in it. calories in and out is the biggest myth you will see and the food companies are laughing to the bank
as far as metabolism, the way you keep your metabolism strong is cycling your calories and carbs daily. if you eat in a deficit everyday you will lower your metabolism. that is what people do not understand. one day you might eat 0 calories, the next you might eat 4000 calories, etc. that is why these crash 500 calorie a day diets the person ends up fatter