Depends on the route and the time of the year you are planning to fly. 2 to 3 months, before the date of the trip for an off season time to NYC (Mid January to mid April), is the sweet spot. For Argentina (EZE) and Uruguay(MVD), 2 months is also perfect. Also take in consideration the day of the week you are trying to fly, Tuesday and Wednesday I always find the best fare for business.
However, at the end of the day, use the Google flight calendar tool, in that way you will always find the best price. You will see the pattern in the timeline and catch the best spot for time.
There are a lot of things to consider that can be specific for a route.