Long Island is an island stretching eastward from New York City in the Metro New York region. The largely suburban area is approximately 115 miles long from Brooklyn and Queens at the western end, to Montauk at the easternmost point. At its widest the island is approximately 20 miles from north to south. While Long Island geographically includes Brooklyn and Queens, politically Long Island in general includes Nassau County and Suffolk County of New York State only.
While Long Island is home to three million year-round locals, many commuting in and out of New York City, the Island is home to a lot of discreet tourism (concentrated in certain towns- Huntington, Fire Island, Montauk) and also serves as the zip code for the vacation homes of many wealthy city dwellers, particularly in the Hamptons.
Long Island is essentially a suburban area throughout (except for the Twin Forks region, which is rural) and has few major cities.
From a tourist's point of view, Long Island is most ideal to visit in the summer and the fall when the scenery can be most appreciated. Long Island is great place to visit whether it be for a family vacation, a group of 20-somethings looking to rent a summer house, or an older retired couple looking to enjoy some natural sight-seeing or tour a museum.
Nassau County and Western Suffolk County is very developed and densely populated, and is home more to the 'suburbia' type neighborhoods Long Island became famous for after World War II, where most year-round residents live. (i.e. Levittown, Oceanside). Central and Eastern Suffolk County, however, is somewhat rural (for the New York area, anyway) and is home to much agriculture, wineries, and beach towns. Many summer homes and hotels are located here, and is where most wealthy New Yorkers congregate in the summer months when the concrete jungle is too hot to bear. Tourist attractions can be found equally in both counties and throughout the entire Island.
Long Island's only downside to tourism is harsh north-eastern winters that make traveling somewhat difficult, and the fact that it is an expensive place to both live as a permanent resident and also as a tourist. There are towns that are more friendly to the wallet than the notoriously expensive Hamptons, or "Gold Coast" North Shore towns, however, Long Island is home to some of the most expensive zip codes in the entire world. Do not expect a bargain vacation when traveling to Long Island, or anywhere in the New York Metropolitan area for that matter.
The Long Island Conventions & Visitors Bureau  provides information about Long Island and the places to visit.
The Long Island Railroad  runs from Pennsylvania Station in Manhattan to various points on Long Island on many branches. Service is not as frequent as the NYC subways. Take the Long Island Rail Road from Penn Station to Long Beach ($8.25 one way during off-peak hours) and from there go south to the beach itself.
When traveling along the North Shore, you may take the scenic and relaxing route of 25-A, a single lane road that runs through historic, wealthy towns on the northern shore.
Long Island Bus has a main terminal in Hempstead. There is also a terminal which serves about 4 or 5 different buses in Mineola that take you to the North Shore.
Long Island Rail Road (which has a major transfer point at the Jamaica LIRR which EVERY train line except Port Washington Branch goes through) can take you to Manhattan, Queens and Brooklyn.
In addition to highways getting into Long Island, there are more to get around:
The Long Island Expressway has the high-occupancy-vehicle (HOV) lanes in both directions in Nassau and western Suffolk Counties. From 6 am to 10 am and 3 pm to 8 pm from Monday to Friday, it can save time for motorcycles (even without passengers) and cars with at least two occupants.
The Meadowbrook Parkway runs from Jones Beach, through Long Beach connecting the south shore towns to Mineola and The Northern Parkway.
The primary tourist attractions are the large number of excellent beaches along Long Island Sound on the North Shore (the setting of the famous novel and movie "The Great Gatsby", and the more famous South Shore, which is home to the Atlantic Ocean's waves and white-sand beaches.
The North Fork is also home to many wineries, farms and culinary outlets.
Other attractions include North Shore harbor towns such as Port Jefferson, Huntington Village, Stony Brook and Northport where a variety of eateries and small businesses thrive in a bohemian atmosphere.
Long Island is also the home to Stony Brook University, one of the top-100 Universities (US News and World Report), which is part of the State University of New York (SUNY) system, providing a very academic and international community within central Long Island. Brookhaven National Laboratory, affiliated with the U.S. Department of Energy, and Cold Spring Harbor Laboratory, (where DNA was discovered by Watson and Crick), is also located on Long Island. Both labs are affiliated with Stony Brook University.
Long Island is a lot like New Jersey and parts of Connecticut in as much as a there are a lot of 24 hour diners that serve pretty much anything whenever. Young people congregate in these diners at odd hours, and they can be found spread out on the major roads like Jericho Turnpike or Sunrise Highway. There are also many seafood restaurants (especially with local clams and mussels-local Long Island specialty foods). Because there are so many local restauraunts, (many Zagat rated), with influence from European families and the nearby international cuisine of New York City, a Long Islander wouldn't recommend to eat at a chain restaurant that could be found anywhere such as Applebee's, the Olive Garden or Red Lobster. They are of course readily available on Long Island, but it is really a shame to not try privatley owned eateries that are equally priced but more distinct than the chain restaurants. Try one of the following:
Many major fast food chains and chain casual dining restaurants have locations on Long Island.
Be sure to visit a local farmstand, especially those out east and on the North Fork. Local produce and farming is a major industry on Long Island.
Drinking on Long Island is tough because you need a car to get around, with this in mind, use the Long Island Railroad to your advantage. Take it from town to town, or take a night out to go into the City. At night, there is little public transportation besides LIRR, but there are taxis. The South Shore in Nassau County has some good bars, (with a somewhat rowdy crowd, however).
On the North Shore you will find a buzzing college-bar scene year-round, mostly for those college students and other 20-somethings looking for a night out that doesn't involve a dorm party, frat or sorority or an expensive trip to NYC. The most popular towns for this kind of bar-scene are Huntington Village, Port Jefferson, (both along Route 25-A) and recently Smithtown along Jericho Turnpike/Route 25, which has developed as an up and coming bar scene by night despite their charming shopping and family-oritented atmospheres by day.
Montauk and Fire Island, which are very much touristy beach towns, are home to many bars- what else is there to do on a warm summer's night?!
Be smart, don't travel to towns with a lot of crime at night. These towns include: Roosevelt, Hempstead, North Amityville, North Baldwin, Wyandanch, Rosedale, North Bay Shore, Central Islip, New Cassel, Brentwood, Uniondale and northern Freeport. In the daytime, these areas are generally safe.
Other than those towns, which most locals could tell you is where most of the dangerous crime occurs, crime on the rest of Long Island is related to drug-arrests and burglarlies of high-end neighborhoods. Most robberies are related to hired help, and are low-profile crimes. However, the most recent epidemic crime problem has been the increase in heroin use among Long Island teens, particularly of wealthier neighborhoods along the North Shore. Generally, this should not be a problem for a tourist.
One of the biggest saftey hazards Long Islanders face when preparing for natural disasters such as hurricanes is the lack of ways to get off the Island. There really is only one immediate way out via car- through the highly congested bridges of New York City. You may also exist via Ferry to New England, or fly out of one of the three major airports. (One on LI, 2 in NYC)
You may leave Long Island to go on day trips to any borough of New York City, Connecticut, New Jersey, upstate New York (another great place to visit)...however, there are so many day trips that can be spent on the Island itself with it's many unique towns and other nooks and crannies, that it is advised by locals to plan on staying on Long Island if you plan a trip here and seep into local life as much as possible. It is very common for Long Islanders to never leave the Island during summer vacations because there is so much to do in the summer even for locals. The Island itself is large, and one csn live on Long Island their entire life and still find something new to do or explore on the very same island each summer. On Long Island, there is no manufactured fun. It is all about exploring the communities and natural scenery for what they are to year-round residents. Long Island is not built for tourists like Florida's Disneyworld might be, however, ironically, that makes for the best kind of tourism.