Uh...have fun?
What are your tastes? Are you young and like clubbing? Then look for some hot dance spots. If you're a bit older and like bars, check out...shoot...I think it's called Kettle of Fish (in Greenwich Village) or Boxers (about a block east of 7th at Barrow). Robert DeNiro and Jessica Lange filmed Night and the City there (nice scene with DeNiro doin' it to her on the wall around the corner from the entrance 🙂 ) There's a Lemongrass Thai food restaurant on the west side of 7th right there near Barrow...good food.
Do you like museums? Definitely take in the MOMA on 53rd between 5th and 6th Ave.
Skip the Hardrocks and Planet Hollywoods...those things are everywhere.
Walk thru Central Park.
Check out the platforms at the WTC site (you won't believe how big that area is once you're there...truly a sad sight...have many memories of that place, myself). You won't be far from Wall Street at that point (it's a little SE of the WTC site)...then head south to Battery Park and take a ferry to the Statue of Liberty. Also, a great way to see the skyline is the Staten Island Ferry. I got some great sunset shots of the Verrazano Narrows bridge and the skyline (with the WTC...this was back in '93) from the deck of the ferry.
Take in a play. You might be able to get tickets to see The Producers. Also, Bat Boy might be still playing at Union Station 😀
Time Square is cool at night. There's Macy's a little south of that, too.
Just have fun and be prepared to walk a LOT.
The wife and I usually stay in Midtown and will walk south down 5th (check out St. Patrick's Cathedral...beautiful and HUGE) and then back up Broadway...back to the hotel to rest and then cab it down 5th to Washington Square (used to see the WTC on the way down 🙁 ) and then walking around Greenwich Village for a restaurant and then a bar (almost anyplace down there is good...check out The English Derby (I think it's on Macdougal near Bleecker...if it's still there).
Another fav of ours is walking up from around Central Park South to the French Roast Cafe (Broadway and...84th, I think). Good food and coffee and some darn good desserts, too