Kabbolas Shabbos should be held early so people do not do melacha too close to Shabbos. Borchu should wait until the time for Krias Shema arrives. Some kehillos make Borchu early as well in order to protect people who are ignorant from doing melacha up until Borchu. When they get home they should repeat Krias Shema. (ShA – MB1)
Every kehilla should have an appointee in charge of announcing the arrival of Shabbos. A half hour before sunset he should announce to everyone to prepare for Shabbos. (Rama – MB1)
Even in large communities, volunteers should go through the street telling people to close the shops and light candles. Their reward for constantly strengthening this mitzva is that their sons will be gedolay Yisroel. (Rama – MB2)