It sounds obvious, but advance planning of more than your airfare and hotel is especially true of a vacation to the Orlando area. Put together itineraries one for the entire trip and one day-by-day including must-see events or attractions as well as a "B list." Check the times of any events you want to catch, like a SeaWorld show or Disney's nightly fireworks. Keep the energy level and attention spans of your kids in mind and consider building in some down time each afternoon to let them (and you) recharge.
If you're visiting Walt Disney World or Universal Orlando, consider which park or parks you want to visit each day. Disney has four parks: Magic Kingdom, Epcot, Hollywood Studios and Animal Kingdom. Universal has two: Universal Studios and Islands of Adventure. Keep in mind that multi-park tickets are more expensive, and that you'll have to build in time for crisscrossing between areas. Buying theme park tickets in advance is cheaper and saves you time waiting in line.
Walt Disney World experiences like Cinderella's Royal Table and the Bibbidi Bobbidi Boutique (which offers "princess makeovers" for kids) take reservations 180 days ahead of time, and they fill up quickly. It's also recommended to reserve early for the Dolphin Swim Experience at SeaWorld's Discovery Cove, Cirque de Soleil and Blue Man Group tickets.
Visit Orlando offers the Magicard, a free pass good for a constantly-changing roster of discounts on everything from museum admission to restaurant dining. You can pick them up at the visitors' center, but save time by printing one online or ordering one that will come in the mail.