I have two boys (currently 11 and 12) and have been to WDW 3 times with them and these are my suggestions:
1. STROLLER; Bring or rent a stroller for your son! On our first trip my sons were 6 and 8 and after the first day at the parks we rented a double stroller every day. Best money we ever spent!!
The parks are big and require a LOT of walking often with crowded walkways. Children got jostled and bumped into. Putting your son in the stroller allows him to take in the sights, get a little rest and most importantly...you won't have to carry him when he gets tired!

We travel the first week of October and on our first trip it was in the 90's. The boys were hot and tired from walking and we'd just put them in the stroller and go. They enjoyed the "sightseeing" and we enjoyed the peace and quiet!
2. RESEARCH, PLAN AND RESEARCH MORE: As others have already said, research, read and plan. While others may prefer to go with a more "loosey goosey" approach, I prefer to plan EVERYTHING. Once I am there, I can always alter the schedule, go with flow or choose to skip an ADR. I do NOT advocate a strict timetable and force marching your child through WDW. However, failure to have a plan will result in frustration and long waits. I feel so sorry for the people I see at WDW looking forlornly at a map or trying to secure a table at a restaurant without ADR's while a screaming, hungry child hangs off their arm.
Planning insures that you have options. You can stick with the plan and know that you have a seat for lunch at Via Napoli at 12:00 for lunch OR if you see a tasty item at a counter service with a short line, you can ditch the ADR and eat at the counter service.
Plan everything, but be willing to ditch the plan when something else great comes along!
I think it's important to have a plan for which park you want to visit each day, where you want to eat and what rides/attractions you want to make sure to do. I even read the menus for each restaurant we plan to visit just to make sure there is something that my children will like to eat. Nothing worse then waiting an hour and a half for a table just to get the menu and find that they have no chicken nuggets and little Johnny eats nothing but chicken nuggets.
I recommend scouring this website as well as
www.allears.net Become familiar with the park layouts to avoid wandering aimlessly looking for rides, bathrooms, etc. Describe the attractions/rides to your son so he can be involved in choosing what to do.
Check
www.allears.net and WDW official websites for closings and rehabs. Nothing worse than telling your son all about Splash Mountain only to arrive at the Magic Kingdom and finding out that it is closed for three months.
3. ARRIVE EARLY, TAKE AN AFTERNOON BREAK AND GO BACK IN THE EVENING. Although I seem to never follow this advice, if you have younger children it is a must. The parks are much less crowded when they first open and swell about lunchtime. Leave at lunch, return to your resort for a nap or swim and then return to the park at dinner. This will increase the odds that your son will make it until the fireworks and most of the parks look beautiful at night.
4. STOP AND SMELL THE ROSES! Honestly, my husband scratched his head in bewilderment at the amount of planning and research I did for our first trip. He thought I had lost my mind. However, once we arrived at WDW he appreciated the depth of my planning. WDW can be very overwhelming...the sheer size of the resort, the number of parks, number of restaurants, etc. Planning helped us avoid arguments born out of frustration.
BUT, despite all my planning I was always willing to alter the plan. If the kids were content watching fish in a pond...I was content to sit with them. We skipped several ADR's and headed back to the resort to swim and play in the arcade. Some of my boys favorite memories are going to the arcade in the evenings with their dad and then heading to the food court right before it closed for milkshakes.
So, relax, stop and watch the fish in the ponds and skip the fireworks to play in the arcade!! Have fun!