How to do a sit up properly for maximum effectiveness and safety?

To do a sit-up properly for maximum effectiveness and safety, lie on your back with your knees bent and feet flat on the floor. Place your hands behind your head or crossed over your chest. Engage your core muscles and slowly lift your upper body off the ground, keeping your back straight. Exhale as you come up and inhale as you lower back down. Avoid pulling on your neck and use controlled movements. Repeat for desired number of repetitions.