[0420wilmut]

Your first time planning will seem very overwhelming.
I'd suggest visiting all the Disney theme parks inc one of their water parks and both Universal parks too.
For our first visit 15 years ago, I purchased A Brits Guide and The Unofficial Guide to Walt Disney books - both gave me a basic understanding of what to expect. It's definitely important for you to have a basic plan for each day. I would advise learning about Disney fastpasses too.
It's very easy to get overwhelmed. A good friend of mine went with her family for the first time recently. She was very overwhelmed before they went - they planed the basics and went with an open mind and quite simply had a ball! They are now saving and planning a second trip with a list of what they want to improve on.
Don't forget you can ask away on here too. Dibbers adore helping newbies and have stacks of advice to give.
Happy planning!