Doing it correctly requires thought, and mindful attention to Posture, Form, Flow, Intensity, and Duration.
Form is always more important than speed.
Form - Posture
Start by standing at attention. Head up straight as if a gold cord goes from the top of your head into your pelvis and down to the earth below. Your chin is parallel to the ground. Eyes fixed on the horizon. Shoulders back and down. Chest out in front as if leading with your heart. Continue this, being mindful of your whole body, checking whether your posture or gait starts to go back to the PD way. If it has downgraded, stop, re-align your body and then continue.
Your body provides proprioceptive feedback to your brain. The more you mindfully walk, more nerves bundle together and reestablish how you would walk as if you didn’t have PD.
This is mindful therapeutic walking. Emphasize the Mindful part first. Walk fast enough that you can still speak normally, but that’s all. Short sentences, not expounding on some subject. This is not for walking the dog. You can’t be mindful of your body if your attention is on the dog looking for the next tree to sniff.
This depends on your fitness level, location, and weather. Start with at least 20 minutes. As you get more fit, gradually extend that time to one hour.
Start formal training three to five days a week. When you are more fit and can cover 3 miles per walk, three days a week is fine.
BUT anytime you're walking, remember to be mindful of your posture and gait.
AND the pace doesn't necessarily have to be swift. FORM first. SPEED second.
"Few people know how to take a walk. The qualifications are endurance, plain clothes, old shoes, an eye for nature, good humor, vast curiosity, good speech, good silence, and nothing too much." ~Ralph Waldo Emerson