Take a large step backwards and space your feet at hip width.
Bend your front leg until it's at roughly 90 degrees and your back knee is close to the floor.
Extend back up to standing and repeat.
Striding too far back.
Too small of a stride back.
Hips caving inwards on the way down.
Holding a kettlebell in one hand, stand with your feet spaced at hip width.
Start by taking a large step backwards with one leg. Bend until your front leg makes a 90 degree angle and your back knee almost reaches the floor. Then drive through your front foot to extend the knee, returning to a standing position. Keep the majority of your weight focused on the front foot as you lower your hips down and bend your front leg. Your front foot should remain flat as you lunge but your back foot's heel will lift off the ground. Repeat for the desired amount of repetitions.
Avoid having your front knee cave inwards past your big toe.
