It's all about supply and demand.
I know it's easier said than done, but planning a year OR MORE out from your desired vacation departure date will help you save money and disappointment in the long run.
This is especially true if you are planning to travel over a "holiday" ... Thanksgiving, Christmas, New Years, Spring Break, Summer. This also applies to traveling to warm/tropical destinations in Winter.
When trying to book something, even six months in advance, your options severely diminish in terms of hotel/resort and flight availability.
And, generally speaking, the closer to the travel date, the higher the prices since demand is increasing and inventory is decreasing.
So, bottom line ... Be an Early Bird and Book Now!