Every day on this site, there are itinerary postings. These range from the good, to the bad, to the just plain ugly. When I travel, I normally do not use a set itinerary, but lots of people do. So, here are some suggestions of what to do - and what NOT to do.
1. "I am coming for three days and want to see everything." You won't and you can't. There is just too much to do and see here for three days. Your options are to skim the surface and race by the exteriors, or take you time and do several things you really want to do each day. I would opt for the latter. You can always come back, we'll still be here.
2. The Laundry List. This is just a list of sites that the visitor wants to go to, in no particular order or geographical sense. New York does not have a central area where all tourist things are. We are spread out, so you have to plan accordingly. Get a map and plot where the items are. Have a downtown day. Spend a day midtown. Museum day. etc.
3. The Overplanner. "We will be at the MET from 10:15 to 11:35 and then head to the Frick from 11:55 to 12:45. Lunch is at...." The fact is that subways, as much as they are the way to get around, do get delayed. More importantly, you will likely see something that makes you want to stay somewhere longer. Allow room for spontaneity. Allow room for relaxation and taking it easy.
4. The HOHO Tourist. I name them after the ubiquitous Hop On Hop Off Buses. These are herd animals who never venture off the designated Gray Line Routes. Now, there is nothing wrong with a bus tour to get your bearings. But, make sure to venture away from the beaten path. Visit Brooklyn - more than just a Bridge and a slice of Pizza. Spend a day at the Bronx Zoo or Botanical Gardens. Visit diverse Jackson Heights and get some great Indian food. Most of all, see real neighborhoods where we actually live. I work downtown - but I live, eat, drink and play in Park Slope.
5. The Slave. The itinerary says that I must go to Central Park now, but it is raining. You are the master of the itinerary and not its slave. If you miss something so be it. If you scrap a whole days plans to just wander around the West Village, the world will still turn on its axis. Adapt.
6. The Chain Gang. People have different interests, and a vacation must cater to everyone. That does not mean that you always have to be together. She can go shopping and he can visit a pub or two. He can see the Yankees and she can visit the Whitney. When you meet up at dinner, exchange stories and swap photos.
I had a professor who told us about the five Ps. Proper Preparation Prevents Poor Performance. Spend you time before coming doing the research. Visit on line sites. Lurk on the Forum or ask questions. Consult guidebooks. Speak to folks who have gone. Make an idea folder.
I hope that this somewhat sarcastic guide helps with your planning. See you in Brooklyn!