This might sound deceptively simple but I’d start by replacing low-nutrient high-calorie foods with lower-calorie, nutrient-dense ones.
Years ago, I too dreamed of getting a flat stomach. One which I didn’t need to sucked in when sitting down. Basically, a stomach that looked good regardless of the rise of my pants or the type of shirt I chose to wear.
I have always been physically active, so I had an feeling that changing my diet was likely to be the solution I was looking for. I just wasn’t sure where to start.