In general, when looking for the cheapest flight to New York, try to choose a flight departing in March for the best deal.
In general, most flyers find the cheapest time to book a flight to New York is about 60 days prior.
From most locations, the cheapest flights to New York are found on a Wednesday. Booking a Sunday departure is usually the most expensive.
On average you can find the best deals on plane tickets to New York when looking for flights with evening departure times.