You're not going to find quahogs in any numbers on the North Shore.
You're best bets for rec shellfishing for softshell (steamers) are Ipswich, Essex, and Gloucester, in that order. It will be expensive for a non-resident license. Certain flats within Plum Island Sound are federal Refuge property and you'll need a license from them too (I believe that its free).
Pay attention to rainfall closures. Sometimes all it takes is 1/4" of rain in a day to close flats down for 3 or more days.
If and once you decide on a town, give the shellfish constable a call, they're all nice guys and they will help you out.
As far as technique, that'll come with time and practice. Try and find a friendly clammer to show you. It's not that hard. Any other questions, send me a PM. I'm sort of in the business.