Andrew McGowan’s Ancient Christian Worship is a very fine introduction to the subject. Though it is up-to-date academically, and, as McGowan says, includes the results of some of his own research, it is accessibly written, clearly organized, and highly informative.
McGowan traces early Christian worship from its origins in the apostolic era through the early fifth century. He is aware of the Jewish context of early Christianity and frequently discusses Christian rites and practices in that context. He also situates early Christian worship in the context of Greco-Roman culture – highlighting, for instance, the continuities and discontinuities between Christian communion meals and meal practices of the Romans, or pointing to the patristic assault on animal sacrifice.After an introductory chapter, the book covers meals, preaching and reading Scripture, singing and the issue of instrumental music, various practices of initiation, prayers, and calendar. Along the way, he finds space for informative treatments of lesser rituals like the kiss of peace or foot-washing.
He is neither a splitter nor a bundler; he recognizes the diversity of early Christian liturgies but also points to overarching commonalities.
There is nothing earth-shattering here, but readers looking for a sure-handed survey of the landscape, this would be a good place to begin.