I would like to know what the procedures are on departing JFK. I'm allowing three hours before my flight.
Will that be enough?
What do I do then?
Where do I find check-in?
Arriving at JFK two hours before your scheduled departure time is sufficient. If you tend to move around more slowly than others, or have quite a lot of luggage, three hours might be prudent, and certainly is sufficient in any case.
Your taxi will drop you off directly in front of the checkin area for your airline (you will need to tell the driver you're flying international, and of course on which airline). From there the process is basically a giant funnel similar to the one you will have endured at Heathrow.