Favorite thing: The best time to visit Orlando is when other people aren't. This would be when U. S. schools are in session, typically September through May, with the exception of school holidays (Christmas, Easter, etc). The weather is still very hot through the end of October, with more moderate temps being November through March. The first 2 weeks of December is a great time to go, especially to Disney World's Epcot, because you get to experience all of the different countries dressed in their holdiay best. Also in the same time period, the days are warm and evenings are cool, so bring a sweatshirt if you are planning a sunup to midnight day out.
Favorite thing: Have a good pair of walking shoes, carry around an umbrella, and carry around a bottle of water. (Expect afternoon thunderstorms in the summer months!)