The dead bug exercise is for beginners and is great for eventually getting flat abs. It’s used a lot in physical therapy and by people who have a weak core. You should be lying on your back; your hands should be reaching up or you can leave them by your side. Bring your knees up forming a 90-degree angle. Start the exercise by extending one leg – straighten the knee and hip. Maintain this position for a few seconds, switch legs and repeat.