Weather is looking pretty good guys. Always a chance of rain on long island during the summer so that's not a big deal. Posted this on the WH boards the other day but some of you might find it helpful as well.
Had a little bit of downtime so I made this map of the area.
http://imgur.com/pbnZi39
Red depicts best methods to enter the main lot. There are two ways to get to the venue if you are coming from the west (which I suspect most of you are), and for those who aren't, it means you live on Long Island (coming from the east end) and you don't need to be told how to get in.
The first way in is to take the Wantagh Parkway south (the redline in the center of your screen running top to bottom). Eventually you will get to a roundabout with a large structure in the middle. You need to wrap around and head east on Ocean Parkway (to the right on the map). You will pass the lot on your left. You need to head down and make a U-turn, and head back west for a few seconds where you will be able to turn into the lot.
The second way in is if you end up taking Ocean Parkway from the west (you'd probably take the Meadowbrook parkway south and merge onto Ocean Parkway east, not depicted on the map). If you are coming in on Ocean Parkway, you simply continue heading east through the round about, then make the u-turn and head into to the lot.
Jones Beach labels their parking lots by field numbers. The two fields designated for parking for the shows are 5 and 4. I cannot stress enough that 5 will be where the tailgating will be. It will eventually fill up. Try and get into 5. 4 is where the few cars that cannot fit into 5 go, and not much goes on there.
The VIP lot is marked in purple on the map. There is a separate entrance for the VIP/Premier Parking. Parking in this area is completely unnecessary for this show, as traffic flows naturally and quickly after the show. One thing to note is that when coming down the parkway to the lot, you will see a ton of signs for venue parking. Just ignore them and take the route I suggested above.
If you are trying to go to the beach during the day, park in either of the lots and walk the blue lines on the map. There is a tunnel that will take you under ocean parkway and right to the beach. It is free. Note, what Long Island considers the beach is the ocean. The venue is in Zack's Bay. You cannot swim in Zack's Bay. If you want to swim go to the beach.
Edit: Also, there is a snack stand and real bathrooms available, but be prepared, lines are very long. I believe they also have some porta potties sprinkled throughout the lot as well.