This drill uses the stability of the wall to allow you to focus on all the details that make a roundhouse kick work. This way, you can strengthen your muscles and improve your neuromuscular connection without being afraid of losing your balance.
Point your standing foot toward the wall, then open your hips as far as you can while also lifting your other leg from the ground. Practice keeping the knee of that leg in one spot and not allowing it to move at all as you slowly fold your lower leg in and out.