If you are renting a car as you leave the airport go to the Grand Central Parkway East. Get off for the Whitestone Bridge. You will pass Cit Field (home of the hapless NY Mets) on your right. Go to the Cross Island Parkway. (you will need to stay to the left and not go on the Whitestone Bridge). Exit for Northern Blvd East. Follow from there to Great Neck.
Please feel free to ask me any questions about the area. I live in Ct. now but I grew up in the area. DS reports also on the 9th.
No matter which way you go you will be in afternoon rush hour traffic at 4 PM, but Northern Blvd will take FOREVER! I know it has a reputation as a parking lot, but I think you will be better off on the LIE. Northern Blvd will be nonstop traffic, along with lights.
My son will be reporting on July 9, too. He will also be at a BBQ on the 8th, but fortunately, we live on Long Island and the traffic is not such a big issue for us, as we are usually travelling against the flow.
You will only be on Northern Blvd. from the Cross Island Parkway to Great Neck. You will not be on 495 at all the way I am suggesting to go.
That time of day is unpredictable as far as traffic.
Picture is worth a thousand words .... Go to Google Maps http://maps.google.com
and select "Get Directions" in the .. From Field.. enter "Laguardia Airport" in the ..To Field.. enter "300 Steamboat Road, Great Neck NY"
From the airport the roads are actually .... Grand Central Parkway (East Bound toward Long Island) to the Whitestone Expressway (to the Bronx-Whitestone Bridge) to the Cross Island Parkway (be sure to exit before you go over the bridge) ... then exit the Cross Island Pkwy at Northern Blvd (NY-25A) East Bound.