Subscribe to the Touring Plans website.
"Touring Plans provides day-by-day recommendations for which parks to see to minimize crowds and waits in line . . . Touring Plans is a company founded by a guy named Len Testa, whose team tracks wait times and crowd levels, and reviews restaurants, hotels, and attractions on property. Testa's staff creates touring plans, or step-by-step suggestions for where to go in the parks that are designed specifically to minimize your wait in line. On the busiest days, they claim that their plans can save you three to four hours of waiting. You can either use their pre-planned outlines or design your own, and you can re-optimize them throughout the day based on what you've experienced and what the crowds are like. Touring Plans can also walk you through Fastpass+ recommendations." — Quora user Michael Lee