Stand with your feet hip-width-distance apart, holding a dumbbell at shoulder level, with palms facing inward.
Slowly bend your knees as if you were going to sit in a chair, keeping all the weight in your heels. Don't let your knees move beyond your toes, and don't let the knees roll out or in. Squat down as low as you can, keeping your head and chest lifted, your spine long, and your shoulders relaxed. Keep your arms steady as you lower down.
Press through your heels, and slowly straighten your legs to stand up. Make sure to keep your spine neutral. Do not round your back. This counts as one rep.