Whether you live here or not, you’re certain to get a more local experience if you “blend,” as Marisa Tomei said to Joe Pesci in “My Cousin Vinny.” To blend is to fit in, so to speak. And, in New York, putting forth your best New York City sensibility counts for a lot.
Let’s start with some of the more obvious “not to do’s” that immediately destroy your New York coolness.
Don’t, under any circumstances, walk the streets of New York City wearing socks and sandals, no matter what the season. Sandals can be fine, but use your judgment as flip flops may be more appropriately left for your beach visits. And, please observe the socks-and-sandals corollary if you’re a male: never wear sandals into fine restaurants, theater, or any other upscale venue. Women have it a bit easier here, as sandals (not flip flops) are acceptable as long as a pedicure has been recently enjoyed.
While on the subject of proper attire in Manhattan, “dressing up” doesn’t necessarily make you appear to be a New Yorker, as many city dwellers have mastered the art of “cool” wearing jeans and an appropriately tailored top and jewelry. 
However, dressing properly is key. Don’t even think about going to theater or Carnegie Hall wearing a T-shirt or shorts. If you must wear sneakers due to inclement weather or for orthopedic needs, that’s fine, but otherwise slide on those closed-toe shoes (men) or strappy sandals, pumps or ballet flats (ladies). If you’re in doubt about the level of attire to wear to a restaurant, call ahead. I can’t think of any restaurant that would be put off by a patron asking whether a jacket was required or whether jeans were acceptable. It’s best to feel a bit overdressed anyhow, rather than be underdressed. This isn’t Dallas, and big hair and huge jewels are anything but de rigueur. Chic and classy go very far here.
Cell phone and camera usage have become a huge problem in the city. Never use your phone in an elevator, answer a call in a theater or restaurant (unless you discreetly excuse yourself to speak in private), or drive with a phone in your hand. We will take action, either legal or civil, for such offenses. If you must take a photo as many foodies (myself included) do, turn off the flash and ask your tablemates if it is OK for you to do so. 
In theaters or cinemas, turn the phone completely off so there’s no chance of even a slight vibration interfering with the performance or of the light causing any sort of distraction to your neighbors.
On a final note, pick up the pace. Manhattan is a busy city with busy people frequenting its sidewalks and spaces. Walking is up-tempo here and strolling three abreast is frowned upon; we need room to pass. The same holds true on escalators; if you feel like taking a leisurely ride to your destination, stay to the right so others can climb ahead.
