This is the Northeast so check the weather before you go as it can be very unpredictable. I think light layers are a good way to go unless it’s deep summer and then I just wear sundresses every day.
Temperatures can swing 30 degrees up and down in a matter of days.
New Yorkers are more fashion-conscious than most other American cities so dress up a bit! No oversize t-shirts and shorts please! The cliché is that we only wear black here and it’s true that we wear more black than a lot of other Americans but color is fine too.
Wear comfortable but fashionable shoes like slouchy boots or cute flats as you will be walking a lot. Since you won’t be in a car much, also make sure to have a big bag. Tourist sites will tell you to wear a backpack but personally, I hink this makes you look like more of a tourist. I carry a big leather purse and stash a rolled up tote bag in my purse for impromptu shopping sprees.
For weekly events, pick up a copy of Time Out New York.
One more thing: New Yorkers aren’t rude, we’re just very busy and direct. We work long hours and don’t get a lot of time to ourselves. Since many of us live in tiny places, we tend to gather outside our homes a lot and run from work to gym to dinner to parties in one day without going home first. So what I am saying is, be nice. Most of the “rude” people I have encountered in Manhattan are actually tourists acting the way they think New Yorkers act.