The preparation phase begins as soon as the previous stroke is completed. Avoid the common beginner’s mistake of releasing the seat too soon and having the knees come up. Take the time to set up the proper sequence so the upper body has more length. You want to arrive at the catch position with shoulders in front of hips, arms stretched and legs at vertical.
You can help create rhythm by ensuring you begin the preparation phase in the ideal position: just past perpendicular, with the core engaged. While this is happening, you still have resistance generated from contact with the foot pad. Avoid leaning too far back. Set yourself up for success for what follows in the stroke sequence.