ive dug a few up on mud flats and marsh banks in some of the back bays but theyre always pretty small, there are different kinds of worms out there that most people dont even know about, google clam worms, a lot of shops used to sell these and they are as good for bait as they are nasty to deal with
Same as most everyone posted find your honey hole at a low tide (outgoing best) gives you more time. Bring a pitchfork and have at it. If digging in an approved clamming area get a license and get some clams also. Adding that in as it is illegal to even harvest bait clams without a license. Or even pick them up off the beach/wash/surf.