Here's this Disney veteran's advice:

1) Budget matters. Is this a $2500 trip or a $10,000 trip? If the former, stay in a condo. (Google it.) Rent a car; they're very cheap in Orlando. Eat a big breakfast outside the parks (I like Waffle House). Carry snacks and get walk-away food. Have no more than one fabulous, themed meal a day. On alternate days do other things besides the theme parks, like walking around the themed hotels (Grand Floridian, Polynesian, Wilderness Lodge, Animal Kingdom Lodge). If it's big budget, stay at a Disney hotel, and make in-park dining reservations.

2) Know if you're visiting during peak or off-season. Short version: summer and Christmas are peak. Consult a guidebook for more detail. If visiting during peak, there are two basic timing strategies: early and late. Depends on your personalities, and also if you are coming from another time zone. Both night people, coming from the West Coast? Stay on Pacific Time, up at 10, bed by 2, hang out at Downtown Disney or Citywalk after parks close. Both morning people, coming from East Coast? Up at 7, bed by 11, be at each park when it opens. Like Apple says, "Think different." If you do what everyone does you will have max waiting (standing).

3) For romantic mood I recommend the bar at Narcoossee's, on the grounds of the Grand Floridian, which has a beautiful view at night of the castle reflected in a lake.

Grand Floridia Resort & Spa - Disney Hotel Reservations Book Online

4) You can't possibly do and see everything so don't try. Save some things for "next time" or "when we have kids."