We plan the dates of our vacation first, then worry how we're getting there, but with my fiancee's and my sister's schedules, when we're going is less flexible than for a single family.
After we get our dates nailed down, we begin planning park days by avoiding parks with morning EMH. I stay with my parents so we can't take advantage of it. Being rope drop people morning EMH puts a huge dent in our plans. I rarely look at crowd calendars as I generally know if it's going to be busy or not, and more than anything they seem to be based off common sense; if MK has morning EMH, for example, it will be marked as a park to avoid on the crowd calendars.
Once we figure out the EMH shuffle, a tentative plan of park days begins to emerge. If there is anything that must be planned well in advance, a Wishes Dessert Party, for example, then that day is decided upon and set in stone, especially after the reservation is booked. We usually go for 10-12 days so there will emerge five or six days that are set in stone, and days that can be shuffled around a bit if we need to switch for a hard to get ADR.
It's a given that we will spend at least two days in MK, two at Epcot, and usually just one day each at HS, AK, Disney Springs, and seasonally, Typhoon Lagoon. We are strongly against park hopping so that cuts down on the planning. It's also a given that we will visit Seaworld and do a more cultural day trip somewhere around Florida. So essentially at this point, knowing what we like to do and what we have to avoid, the vacation practically plans itself.
As far as days that can be shuffled, there's still always a main plan with park days mapped out and several contigency plans, so even the shuffling is planned out to a T.
I mess with ADRs all the way up until I go, though. Not staying on site means I have to work harder to secure some of my ressies.
If it's a ridiculously busy time of year (Christmas, 4th of July, etc.) I will also plan out ride by ride, each day in the parks, especially MK.