Start by putting in as much time as you can comfortably handle -- 15 minutes a session, three sessions a week if you can do it, less if you can't. Each week, add 2 minutes to your workouts until you reach 30 minutes per session; you'll then be meeting the 90-minutes-a-week minimum requirement. Consider getting a workout partner, too; having someone to whom you're accountable can really help keep you on track. If you prefer to count steps to satisfy the aerobic requirement, increase your steps per day, working up to over 6,000 daily.
Find out more about this book:The Best Life Guide to Managing Diabetes and Pre-Diabetes