Hi Angie,
I think it is very important to make your dining reservations in advance. Many Disney restaurants are extremely popular and book well in advance. Dining reservations ca now be made 180 days in advance, either online or by calling 407-939-3463. The Disney World calendar indicating park hours is also available up to 180 days in advance and can be found
here.
I typically write a list of the restaurants we want, and then a separate list of which days I hope to visit which park. I match my restaraunt list to my planning calendar and start there. When i call to make my dining reservations, if I can not get my restaraunt choice for a specific day, I either move to our second restaraunt choice at the same park. If the restaraunt is very popular, or one of our absolute favorites, and there is an opening for that location on a different day, then I re-arrange which day I will go to which park.
Although I generally try and plan which park we are at to match my dining choices, we have at times, visited a park for just our reservation and then moved on to another park to play. This is one of the great advantages of the park hopper option.
Hope this helps. Happy planning!