For us, the planning boils down to these basics:
On-site or Off-site?
Everyone has their preferences. You'll find lots of threads on the Dis on the pros and cons of each. For us, after our very first trip to WDW years ago where we stayed off-site, we have always stay on-site. We love being totally immersed in Disney.
Which resort?
This may depend on many factors, such as the ages of the kids when going to WDW, your budget, what themes you like. If you have a sky-high budget, you may want to head straight to the deluxe resorts (think Grand Floridian

, Beach Club

). There are moderate resorts and value resorts - something for all budgets. If you have small children, you may want to stay on a monorail resort such as Polynesian or Contemporary to be close to Magic Kingdom as it has more rides for younger kids. Also, it depends on what the family is into, for example, Animal Kingdom if you want to be in a safari-like setting, All-Star Sports if they're into sports themes, All-Star Music if they like music, etc.
Free dining Plan?
Do you plan on doing more sit-down dinners or all counter service? Do you have kids who like to eat or kids who are picky with the food? We have a tweenie and a teen who like to stop and eat, and aren't picky, so we always opt to go during free dining. It is so worth it for us to have that included in our package.
Time of Year to Go?
We always pick end of August. Pros are that it's not crowded because a lot of U.S. kids are back in school, our kids are still on summer vacation, the resort rates aren't expensive, free dining is ON, and airfares are OK. Cons are that it's hot and humid. But then, Christmas is also such a lovely time of year to go too albeit crowded and expensive. Spring break is crowded but the weather is so much more comfortable.
Rent a Car or Not?
We always rent a car, because we feel that time is never on our side. We also like to make side trips to the Super Target and to the outlets, so the car comes in handy. Disney has good transportation onsite, which is fine for a lot of folks.
Hope this helps and doesn't confuse you even further

! Happy planning!!!