So great that you're thinking ahead!
*Know your time frames - packages usually come out in August for the following year, so be ready. Know when your 180 days for dining reservations will open and make sure you've already researched the restaurants leading up to that date. (I always reference the menus on allears.net.)
*Start a Disney box or drawer - I throw in travel size stuff throughout the year so that by the time we go, we have everything we need. Don't forget to add band aids and blister block and sunscreen.
*I agree about making an ongoing list of tips you read on the Dis! Helpful things I learned early on: free water at CS restaurants!
*I also agree about starting your walking regimen now. Seriously - you will walk MILES every day in Disney.
*My grandparents always did a GREAT thing when prepping us for our childhood trips. (We were quite young when we started going.) Mom-mom always reminded us that when we were in Disney, we were going to be waiting in some lines and that's just the way it is. She seriously reminded us
EVERY time we spent the weekend at their house for
MONTHS leading up to our trips. But, you know what? By the time we were in Disney, we knew we'd be waiting in lines, because that's one of the things you do at Disney. (And those were the pre-Fastpass days, so there were some LONG lines!) As a result, we never pitched a fit about having to wait in line when we were little - on any of our trips (at least that I can remember

) She's already started prepping my nieces in that way for
their first trip next summer (Aug.2012.)
*Start thinking of a BASIC priority list of what's important to your family - read up on the different attractions and decide what you really want to do.
*Start to think about shopping for some really good walking shoes. I know some people like sneakers, but I can't even THINK of wearing closed toe shoes to Disney. I've invested in some really good walking sandals - Eccos and Keens. I alternate those every other day - for our heavy walking that we do in the mornings. I also take my Reef flip flops to wear in the evenings. I find them to be super comfy.
*Make sure you understand Fast Pass. This will save you valuable time and sanity.