Recommendation: travel guide "Eyewitness Travel's Top 10 New York City" by Elenor Berman. Published by DK Publishing (I bought it at Barnes & Noble). There are "Top 10's" for every borough/neighborhood, plus other tips & tricks, plus a pull-out map. I memorized it before I went.
Looooooved NYC! Was there last September for a couple of my BFF's wedding so we were on a tight schedule but saw as much as possible. Amazingly enough, Manhattan is very walkable and you can do quite a bit in one day.
If you're worried about how to get around, the subway system was VERY easy for me to navigate. Let me preface this by saying, it's incredibly hard for me to get lost but...There are maps in every terminal and the stop is announced before every stop, either by conductor or electronically on the train, depending on what line you're on.
I think we bought a week pass for around $25 for unlimited service. And the subway is NOT scary (I was worried, as I am kind of a country mouse). We stayed with friends in Brooklyn (Bayridge) so we were on the train quite a bit.
A few highlights:
Ground Zero - As an American, this was at the top of my list to visit. No words can describe.
Battery Park - you can catch a ferry to the Statue of Liberty, which we did not have time to do, but you can still see it from the park.
Wall Street/NYSE/South Street Seaport - Pretty cool area to see. And the bull sculpture is literally in the middle of the Avenue of the Americas on the way to Battery Park. The seaport area is on the river, you can see the Brooklyn Bridge. There is a good pub down there called the Heartland Brewery.
City Hall area - I can't even describe how cool it was when I got to see Manhattan's City Hall (I'm a nerdy city planner, myself). And my friends got married in a building nearby and one of the buildings they use for the show Law & Order was there. In general it was awesome to see buildings that I've seen used in movies & tv shows.
Central Park - walked all around from the south end up to the Museum. Incredible public space. God bless Fredrick Law Olmstead.
Tiffany & Co. (bought a souvenier there - and it's right by Central Park & the Apple Store which is cool to see. And the Plaza Hotel is right there, too.)
Chinatown/Little Italy - The San Genarro festival was going on while we were there and we ate in Chinatown (I wish we would've eaten in Little Italy, haha!)
Rockefeller Plaza - My friend and I decided to do The Top of The Rock. I'm glad we did. It was only ~$20 and totally worth every penny of the views of the Empire State building, Central Park, and the surrounding area. Incredible. Incredible. Incredible.
Times Square - Heart of the city. Lots to take in. I suggest going in to M&M world for a delicious experience.
Macy's - We walked from Macy's to Times Square no problems. Go to the back of Macy's to see the world's oldest working wooden escalator (fun to say you've rode it).
Bryant Park/NYC Library - I wanted to go in the library and reenact Ghostbusters but we didn't have time. Bryant Park is a great outdoor space to witness. And if you're a fan of Project Runway, well...then...it's legendary. I almost wet my pants when I saw Parsons and I kept my eyes peeled for "Mood" (never saw it).
Much, much more. I want to go back soooo badly.