In general, when booking your flight to New York, March is the cheapest month on average.
From most locations, booking your flights to New York around 60 days prior to your departure date finds the best deals.
On average, the cheapest flights to New York are found when departing on a Tuesday. Try to avoid departing on a Sunday, as this is usually the most expensive day.
On average you can find the best deals on plane tickets to New York when looking for flights with midday departure times.