I think it depends on so many things.
Are you doing everything separately ie travel, then hotel, then park tickets? Or intending doing a whole package?
My first trip, I booked the flights 6 months before I went, then booked the Disney hotel/tickets package about 1 month before.
2nd trip, I booked the flights again 6 months in advance, and also booked the hotel/tickets package about 6 months ahead, to get an early booker bargain with Disney direct.
Most recent trip (kind of a spur of the moment thing), booked flights 3 weeks before travel, and hotel 2 weeks before (had AP's by then, so didn't need to worry about park tickets, and also got a great discount on the room only price at a Disney hotel).
I think, if you see a price now that you think is a good deal, book it now. Travelling there will probably not decrease in price, but may well increase, the closer you get to your preferred date.
Elaine