This article offers some pretty good tips for people who are travelling to New York City for the first time: http://gridskipper.com/349645/18-steps-to-having-a-good-first-trip-to-new-york

The article is well worth reading, but here's the executive summary:

1. Don't Just Stand There, Ask for Directions.
2. Fear Not the Subway.
3. Wear Black.
4. Just Pick One or Two Tourist Places.
5. In Manhattan, There is No Such Thing as North or South.
6. There is Nothing in the World Slower than a Cross-Town Bus.
7. Get the Hell out of Midtown.
8. Be Cool With the Gawking.
9. Identify and Avoid Freaks.
10. Make the Chain Stores Work for You.
11. What's a Bodega?
12. Respect the Flow.
13. Have a Bagel.
14. As Far As Restaurants Are Concerned, Be Prepared to Pay.
15. Oversized Umbrellas Have No Place on Manhattan Sidewalks.
16. Broadway Is Fine, But Off-Broadway Is Easier, Cheaper, and Often Better.
17. Don't Linger Too Long at Any One Bar
18. Brooklyn Rules.

You are now ready for travel to New York. Enjoy.