Assuming you mean "Plum Island," the best source of fishing info is the fishing report from a famous fishing store up there:
http://www.surflandbt.com/fishing-reports/
If you spend some money there, they'll also hook you up with some ideas on tackle and locations.
That is one of the places I fish every year and I always catch a good number of stripers in the 20-30inch range...but other people (with lots of patience and mainly willing to fish late at night) get some big ones.
Good Luck!
Brian