My personal tips for New York:
1. Buy the 'New York Time Out' (weekly journal which is sold every thursday and gives you the most important info)
2. Make the trip AROUND Manhattan (not only halfway around)
3. When going with the metro, take one of the blue lines (A,C or E) and get out at 4th. The subway is full of little bronze statues
4. Go to on 'Top of the Rocks'
5. In the smaller streets just walk into neighbourhood-pubs
6. In the summer time in the evenings it is great at Southstreet seaport. They have Live-Concerts there and there is always a cool breeze. They used to have concerts between the two WTC towers too which I loved but for obvious reasons they don't to them any no longer
7. Watch the sunset being mirrored in the windows of the Wintergarden of the WTC
8. When it's raining get Umbrella bags inside the WTC-complex
9. For shopping: Century 21 (don't look for something specific though), J & R, Virgin Records
10. Enjoy a leisure summer sunday at Central Park
11. Don't stay in the main tourist areas but go to other boroughs too
12. Take a tour with http://www.harlemspirituals.com/ to Harlem and the Bronx, you will be surprised how nice those boroughs are. If you have the chance to do it with a gospel brunch at The Cotton Club DO it...
13. In the summer take the subway to go to Coney Island.
14. Visit one of the Cemeteries
15. If you have to go by subway on a weekend watch out for white or green Subway-signs, the red ones tell you that station is closed (sometimes it takes you a LOT of time to find a subway station....) And make sure there are no interruptions of service on the line you need to use for that weekend (see top 1.)
16. Visit the Museum of Natural History (especially if you go with children)
17. Take the subway to Brooklyn and walk to Brooklyn Heights
18. Be carefull in Little Italy. a lot of the restaurants are not good.
19. Take your time...