I teach 'quiet' or 'enough' because 'no' can be way overused. If he is treat motiviated then you could teach him a 'quiet' command and when he is quiet, give him a treat. Branch that out to have strangers give him a treat when he stops barking. Soon enough he'll see people and he might bark but he'll quickly stop because he wants his treat. It might just be excitement that he doesn't know what to do with. You will need to teach him how you want him to respond in those situations.
Darby is VERY talkative and she barks and barks and barks when we get home or have a visitor. We're teaching her to tone it down and allowing her to 'woo' instead. She is so funny because sometimes she'll catch herself barking and run and grab a toy and do this wierd vibrating wooish noise because she can't bark with a toy in her mouth.