We always start to talk about our trip early on. We go every year for Xmas and we actually start talking about next year during the last few days of the trip.
It always goes the same way... we say "we better enjoy the trip this year because who knows what next year will bring?!"
Then: "we need to start traveling to new places. For all the money we spend on Disney, we could see the world!"
Then the trip starts nearing and we start planning our moves - the food we wanna eat, our rides, etc.
Then 12/30 hits and we start to get sad. We start saying "well maybe we'll do a short trip next year." Then we start talking about what we'd do.
Long story short, the same vicious cycle has taken place for the past 4 years. We've gone back every year.
As far as planning, I'd say around 250-300 days out you should start to plan. Start to check your finances, get your budget intact, decide where and when you wanna stay.
By 200 days out, I'd personally like to be booked — my resort, my park tickets, etc. Usually flights are announced 200 days out (for Southwest, at least.) We fly Southwest as it's the best value (IMO), we have the points from our credit cards and you can modify your trip if the fare drops.
Also around 200 days out, you can start discussing your dining. Whether you do the
DDP or not, you should start to look into restaurants. With planning out your restaurants, whether you like it or not, comes planning out your parks. You're not gonna book Tusker House when you plan on going to Magic Kingdom, for example. Parks and ADRs is kind of like the chicken or the egg argument.
At 180 days book your FP+.
Around 80-100 days, start to plan out your days. "Okay, we have an ADR for Crystal Palace, so we'll go to MK that day." ... "okay, so we'll need FP+'s for these rides..."
At 60 days book your FP+... then the waiting game starts.
From there on, it's a gigantic game of checking the park hours and eventually the weather. And round and round we go....