Here we have a description of Justin Martyr worship in house churches in the Early Church. "On the day called Sunday, there is a meeting for all in one place, according to the city or town where one lives. The "Memoirs of the Apostles" (i.e. the Gospels), or the "Writings of the Prophets", are read as long as there is time. When the reader has finished, the President, in a sermon, calls us all to imitate these good things. Then we all stand and pray."
Justin Martyr describes the leader of worship as "president" because non-Christians might not understand special words such as "bishop" or "presbyter." John Foster in "The First Advance - Church History 1: AD 29-500" wrote, "The three items mentioned, reading of Scripture, a sermon based on the reading, and prayers (which were said standing), follow the custom of the synagogue. Justin Martyr describes the New Testament lesson as being from the Gospels (and puts this first), and the Old Testament lesson as an alternative, from the Prophets." See also Justin Martyr's Interview which sheds further light on Early Church worship.