How exciting!
WDW is huge, and must-dos vary based on a lot of factors.
Before offering suggestions, I'd like to know what planning you've done so far. Where are you staying? What kinds of rides/attractions do you prefer-- thrill rides, dark rides, shows, "street" entertainment, all of the above? What parks do you plan to visit-- there are four on WDW property, plus two water parks, and the Disney Speings shopping area. What Fastpasses do you plan to schedule or have you scheduled? How important is dining to you? What kinds of dining options do you prefer? Budget is also a factor, but for all of these questions, share only what you're comfortable with.
Absent this information, I'd recommend googling lists of WDW attractions by park and seeing what interest you. Use this information to make your FP reservations at 60 days out of staying on property and 30 days out if staying off property. There's a whole sub-forum here dedicated to FP strategies. If you haven't done so, decide which park you're going to in what day (easywdw has calendars with recommended parks). And if dining is a priority, look at menus for restsramts in parks and make ADRs.