HM79,
I understand how busy and stressful it must be working as a ground controller in JFK, however I believe a lot of the problem stems from the fact that usually the same instructions are issued to local carriers as the long haul internationals.
If a longhaul carrier has 2 flights a day into JFK, it could have been many months since the flight crew has operated there, and to expect them to know the nuances of the taxiway system is unrealistic.
Added to that, the (sometimes) lack of standard phraseology gets very confusing. I am a native English speaker, however I have found the instructions issued on the ground frequency (including at LAX... not just a JFK thing) very non-standard and confusing.
If you wish to improve the service, I think a much more realistic expectation of peoples ability to understand your instruction at the pace that you give them would help. After 16 hours on the flight deck, your brain doesn't work fast enough to comprehend some of the instructions given at the speed of light.
I understand that it is a busy environment, but perhaps put yourself in the shoes of the guys trying to navigate a very large aircraft (larger than the airport is designed for) around a complex and poorly signposted taxiway system, and just slow things down for them a bit. Speak as fast and as loosely as you like for the local carriers, but use the old KISS principle for those that aren't regulars at the airport.