Bend your knees and slowly lower your hips as if to "sit" on an invisible chair. Look straight ahead, keeping your back straight and chin up throughout the movement. Keeping your spine aligned, bend at your knees as if you were lowering toward sitting down in a chair. Keep your heels on the floor.
Do not rock your knees forward at the ankles.
Do not curve or bow your back either forward or backward.
Keep your head up and your shoulders solid.
Only go as far as you can comfortably go toward chair seat level. You'll get nearer there as you get stronger.