The most important tip for visitors is NEVER GET IN ANYTHING BUT A YELLOW CAB!
There are three different kinds of taxis in New York. Yellow cabs can pick up people from the street or from taxi lines at airports and train stations. They have meters that tick off the price as you travel (or sit in traffic). There are also town car services that are usually black or silver town cars. Unlike the yellow cabs, which all cruise the streets as independent agents, town cars work for companies and the only legal way to hire one is to call the company and arrange a pick up. However, these “gypsy cabs” as many NYC residents call them, often cruise the streets for desperate fares and harass travelers at airports. No matter how easy it may seem, do not get in these cabs. They have no meters and therefore you will most likely be quoted an outrageous price as the driver’s take advantage of traveler’s lack of local knowledge. The third kind is also a brand new hybrid taxi designed for residents of the more far-flung Outer Boroughs. It looks just like a regular taxi except it's neon green, not yellow (the City prefers the color be called "apple green"). It has a meter with the same prices as the yellows. So what's the problem? To make sure that these taxis serve only Outer Borough and Upper Manhattan neighborhoods their meters are locked off while the cab is south of 96th street in Manhattan. So the driver probably won't stop for a tourist in Manhattan anyway, but don't get in one all the same. Their meter won't work and you might be taken for a ride.
So, you’re going to get a yellow cab right? Good. Now what are the tricks of the hail? First, look to the top of the cab, there is a light featuring the cabs medallion number. It’s a the 4-digit alphanumeric code that identifies that vehicle. If that light is on, the cab is available. Stick your arm out and it should pull right over. If the light is dark, the cab is occupied and you can keep your arm at your side. When you get in an available cab, the driver is required to take you anywhere in the city. Sometimes a driver will argue that he won’t take you somewhere. Just stand firm and say that he is required to take you and if he refuses, you will call 311 (the NYC municipal switchboard) and report him. Don’t let cabbies push you around!
There a few things that can help you make your taxi experience smoother. Taxi drivers usually work a 4 AM to 4 PM shift, or vice versa. That means that finding an available cab gets much harder around 4 o’clock in the afternoon (or morning if that’s more your time of activity). In fact, lots of drivers on their way home at 4 will have their light off but still stop to see if you're going the same way as they are. This isn't really legal, but it might be the only way to get a fare around 4 PM. Secondly, If you can hail a cab on a street with traffic moving the direction you want to go, that will cut your fare significantly because the driver won’t have to turn around. Thirdly, try to know the cross streets of your destination (i.e. 59th and Lexington for Bloomingdales). Cabbies often don’t know the location of exact addresses, but they should always know an intersection. Lastly, cabbies have a hard job. Many work 60-70 hours a week behind the wheel. As long as they get you to your destination without fuss or confusion, do tip them 15-20%. I know they sometimes seem untalkative and unpleasant, but they aren’t tour guides, they’re drivers. Tip for a successful ride.