Being that the limit is 2 at 12" it's not very hard. In the early spring anchor up in shallow flats like outside of Keyport in the Raritan Bay. Stir up the bottom with a long pole with a plunger attached to the end is one option. A chum pot deployed to the bottom filled with corn and other stinky stuff like dog food works. Small long shank j hooks with a couple of yellow beads work well and the bait of choice is sand and bloodworms.
I believe a thread already exists on this subject. You can purchase flounder rigs at a bait shop.