Holding the barbell (or two dumbbells), keep your arms straight and knees slightly bent.
Slowly bend at your hip joint, not your waist, and lower the barbell as far as possible without rounding your back, which should remain straight. Make sure you keep your spine neutral with a natural low-back arch with shoulders down.
Keep the barbell close to your legs, almost touching them.
Squeeze your glutes to pull yourself up at a quicker pace than when you bent down (beginners should aim to take four seconds to bend down and two seconds to pull up). Don't use your back and do not round your spine.