I like to start my planning with a simple chart, with columns for: Date / Destinations / Meals / Itinerary Summary.
I use 3 rows for each date: one for the morning, one for afternoon, and one for evening. I don't use any fancy software: I just make a "Table" in MS Word.
Once the chart is set up with dates/times of day, I move on to the "Destinations" column. First, I add in our travel plans with expected arrival and departure times (e.g., "BUF to MCO, 7am-10am").
Then, using a crowd calendar with projected park hours (from touringplans, to which I subscribe, but there are other sources out there - at the very least, you can use the hours from the previous year on your dates/days of the week as starting point), and taking into consideration any extended evening hours and special events, I decide which park or parks would be the best ones to visit each day. We usually have parkhopper tickets and tour in two blocks: rope drop through lunchtime, and 4pm to close, separated by a nap/swim break at the hotel in the middle. That means we'll visit either one or two parks per day. I also try to keep in mind the timing of extra evening hours (if we're eligible) and any nighttime entertainment we plan to see, so I can ensure we're not staying up late one night, and then having to get up super-early the next morning. Once I know where we plan to be, I list the parks we're headed to (and their hours) in that second column, "Destinations," for each morning/afternoon/evening time block. Then I make park reservations for the first park we'll be visiting each day
I also like to color-code the Destinations entries with a highlight color, different for each park, so I can see at a glance how many times we plan to visit each one. For no particular reason, MK is always pink, EPCOT is always baby blue, AK is light green, and HS is pale yellow.
Once we have the "Destinations" column done, we can turn to the "Meals" column, and start figuring out what nearby places we want to eat. We usually do breakfast in the hotel room, and have 1 CS and 1 TS for lunch and dinner. Everybody in the family gets to choose at least 1 TS that they want to visit, so I try to fit those in with the pre-existing "destination" schedule so that we're never having to travel far to get to a desired restaurant. Once those plans are made, I fill in the third column, "Meals," with our plans. Then I calendar our date(s) for making dining reservations, and jot down a list of the restaurants and times we want, with alternative choices for anything that is likely to be hard to get.
Finally, I fill out the "Itinerary Summary" column with our travel arrangements and timeline for arrival/departure days, and for the rest of the time, a realistic idea of what we can expect to do during each portion of each day (e.g., 7am: Join TRON virtual queue if available. Arrive at MK by 8am for 8:30am early entry. Tour Tomorrowland and "anytime attractions" in Fantasyland. TS lunch at Skipper Canteen, ADR ~12pm. Return to hotel for nap/swim break. Head to EPCOT, arriving by 5pm. Tour Future World (CS dinner). Park closes at 9pm.) If we're doing any other "scheduled" or simply necessary activities -- e.g., a "Behind the Seeds" tour at EPCOT, or a load of laundry mid-trip -- I include these in the summary, and calendar a reminder to make any needed arrangements
Once my chart is done -- at least 6 months ahead of the trip -- I return to it about once a month (and repeatedly in the last 1-2 weeks before we travel) to note any changes to park hours, special events, flight time shifts, dining reservations, etc. and then modify the other components accordingly, as needed.
As an example, here's an old one from February 2020, shortly before COVID shut things down, when everything -- including WDW -- was a bit simpler. Some of the information (e.g., references to DME, no reference to park reservations) is outdated now and it looks like my headings used to be a little different, but in case my explanations of rows and columns didn't make sense, hopefully this helps:
View attachment 691511