One of the biggest things I was looking forward to when I moved to Orlando was going to Walt Disney World during “slow season.” However, I was not terribly surprised to see there really is no slower season in Disney anymore. No one wants to go there when it’s really crowded. But a lot of people do!
There seem to be small pockets of quieter times in the parks but not weeks or even days of it. I’ve found that sometimes on a Friday night after Wishes Fireworks, the Magic Kingdom gets a little less crowded and the wait time for Pirates of the Caribbean goes back to the 5-minute wait time Disney fans know and love. And a random day here and there you may find less crowded. But for the most part, Disney has succeeded in driving business to the parks.
You could steer clear of the obvious busy time such as holidays. And Saturday night in the Magic Kingdom is never a good idea if you don’t like crowds. But now in addition to those times there are marathon weekends, and seasons of busy time like Epcot International Flower and Garden Festival (going on now!) and Food and Wine Festival in the fall.
Your best bet might just be to have a plan when you go. Use the Fast Pass system because it works! And I’ve always found the World Showcase in Epcot to be a nice place to spend time when there are long lines for attractions. It’s a great place to enjoy an adult beverage, see entertainment on a less crowded level and enjoy a variety of culinary delights!