It's all about the budget.
First of all, if you stay onsite, get the meal plan. It is so worth it and convenient.
Second, if you stay onsite in a value priced hotel (say Pop Culture - a really good one), then if you can afford to rent a car and drive yourself, you will save a lot of time. The bus can be difficult. It's a schlep to get to them and there is often standing room only. My poor husband was carrying a sleeping 5 year old on the bus at midnight and no one would give up a seat to him.
If you can, go high end and stay on the monorail. Personally, I'd rather spend my money elsewhere - you are rarely in the hotel room and when you are there, you are sleeping and praying (for your feet to stop hurting).
Go early to all parks. Don't sleep in if possible.
Plan, plan, plan. I am a planner and it served us well. Plan which park you are going to and on which day and which places you want to reserve meals at.
Go during off peak times. We went in October last year and it was really good weather and not too packed. I hear that going the first week of December is the best time to go - as there are very few crowds. Next time we go, it will be then.
Plan a mid day nap. Your 4 year old will need it.
Buy the book, The unofficial Guide to Disney World. It's packed with great info!
Have fun!!!!