This whole thread has so much good advice so I'll try not to repeat.
We did a "once-and-done" trip for our family of 5 a few years ago and it should be no surprise that we are going again! lol. Expect to love it!
However, with the mindset it was our one and only trip, I needed to plan stuff out and make sure we had no regrets and didn't feel like we wasted money. Doing my homework made that trip a complete success!
1) The planning felt very overwhelming at first. My advice is pick a topic to research and make notes. Then move on to the next topic and repeat. Once you've gotten your feet under you, circle back and make decisions with everything in mind. I felt like everything was so interconnected (times, dining options, rides, travel, etc) that once I had a feel for everything, I could make informed decisions.
2) On the shoes topic - wear moleskin BEFORE your feet/toes hurt. I usually forget/am too optimistic and only remember once I'm already developing blisters. Putting moleskin on top of blisters can make them worse. We just did 2 days at
Disneyland/DCA this weekend and I have double blisters on my pinky toes. One from the 1st day and one from the second. I put moleskin on my heels but didn't protect my toes. I hobbled all the 2nd day!
3) TouringPlans.com is the best $18 you'll ever spend if you're a planner. As a newbie I needed to know what plans were even "do-able". It's pretty darn accurate. It allowed me to switch from thinking we'd do a high priority circle of the park and then a lower priority circle of the park, to a plan where we'd just go through the park once and get our whole list done. Really reduced the back and forth walking. The parks are big! We bounced all over DL/DCA this weekend and did 13 miles each day. We easily did 13 miles at each WDW park with very little zigzagging. I'd bet we'd have doubled it without planning. Even if you don't plan out your whole itinerary, you can get a feel for what you'll be able to do and not do. If you do plan, plan in cushion time. Put in snacks and bathroom breaks so you can be flexible.
4) Ropedropping is a pain but soooo worth it! I'm not a morning person. And my kids do NOT move fast. But it lets you do so much more before the lines get nuts. Without FP, I think RDing is even more vital.
5) Plan a rest day! We did 3 days in parks, a pool/disney springs day, and then 2 more days.
6) Ultimately I think your attitude/expectations make the trip. See what you can, don't regret what you didn't, expect to wait in lines, expect to spend a lot of food, etc. This weekend I spoke to people who bemoaned how crowded DL/DCA was and that it wasn't much fun and then I spoke to people who were determined to enjoy it for what it was and did! At the worst day in the parks, you're still at Disney! There are worse places you could be! =)