First things first: Get a good WDW guidebook. I think you'll see the most recommendations here for The Unofficial Guide - it's like the "War and Peace" of guidebooks (huge), but thorough and an entertaining read. I also still like the Birnbaum's/Official guide for "just the facts."
The most important thing to do is get familiar with the parks and attractions and set your absolute must-do priorities. 3 park days isn't much. Also note that you will need a Park Hopper ticket to enter more than one park on the same day. (You mention splitting a day between AK and DHS.)
Next advice, hang out on the Dis! Check out the restaurants board for opinions on where to eat - I think that is almost the most personal thing, because we all like different places. It also depends on whether you're looking for character meals, signature dining, traditional meat-and-potatoes or something more adventurous. This site as well as allears.net has lots of menus to give you an idea of what's available.
The fun of going solo is that you don't have to worry about what other people want to do. If something sounds fun and interesting, give it a try.
That's just a basic starting point, but researching and planning a WDW trip is half the fun!