Holding a barbell, two dumbbells at your side, or another weight, keep your arms straight and knees slightly bent.
Slowly bend at your hips, not your waist, and lower the weights as far as possible without rounding your back, which should remain straight. Looking forward, not at the ground, will help you avoid rounding your back. Keep the weights close to your legs.
Squeeze your glutes to slowly pull yourself up. This counts as one rep.