Here are some excerpts from ancient writings that talk about ancient religion.
Diana, we are in your care, we chaste girls and boys. Come, chaste boys and girls, let us sing in praise of Diana.
O daughter of Leto, mighty offspring of mightiest Jupiter, you who were born beside the Delian olive tree, queen of the mountains and the green forests and the trackless glens and the murmuring streams.
You are called Juno Lucina by women in the agony of childbirth. You are called powerful Trivia. You are called Luna, with your borrowed light.
You, goddess, measuring out the year's progress by your monthly phases, do fill the farmer's humble storerooms with fine produce.
Hallowed be thy name, whatever name it is that you prefer. And, as in years past you have been accustomed to do, so now, too, protect and preserve the race of Romulus with your kindly favor.
This excerpt from Pliny the Elder tells of the importance of rituals being performed very carefully and accurately:
It apparently does no good to offer a sacrifice or to consult the gods with due ceremony unless you also speak words of prayer. In addition, some words are appropriate for seeking favorable omens, others for warding off evil, and still others for securing help. We notice, for example, that our highest magistrates make appeals to the gods with specific and set prayers. And in order that no word be omitted or spoken out of turn, one attendant reads the prayer from a book, another is assigned to check it closely, a third is appointed to enforce silence. In addition, a flutist plays to block out any extraneous sounds. There are recorded remarkable cases where either ill-omened noises have interrupted and ruined the ritual or an error has been made in the strict wording of the prayer.
Cato the elder tells how a prayer and sacrifice should be made before harvest:
Before you harvest your crops, you should offer a sow as a preliminary sacrifice in the following manner. Offer a sow to Ceres before you store up the following crops: spelt, wheat, barley, beans, and rape seed. Before you slaughter the sow, invoke Janus, Jupiter, and Juno, offering incense and wine.
Offer sacrificial crackers to Janus with the following words: "Father Janus, in offering to you these sacrificial crackers I humbly pray that you may be benevolent and well disposed toward me and my children and my home and my family."
Offer an oblation cracker to Jupiter and honor him with the following words: "Jupiter, in offering to you this oblation cracker I humbly pray that you may be benevolent and well disposed toward me and my children and my home and my family, being honored by this oblation cracker."
Afterward offer wine to Janus with the following words: "Father Janus, just as I humbly prayed when I offered to you the sacrificial crackers, so now for the same purpose be honored with sacrificial wine."
And afterward offer wine to Jupiter with the following words: "Jupiter, be honored by the oblation cracker, be honored by the sacrificial wine."
And then slaughter the sow as a preliminary sacrifice. When the internal organs have been cut out, offer sacrificial crackers to Janus and honor him in the same terms as when you earlier offered him crackers. Offer an oblation cracker to Jupiter and honor him in the same terms as before. Likewise, offer wine to Janus and offer wine to Jupiter in the same terms as it was offered when you earlier offered the sacrificial crackers and the oblation crackers. Afterward offer the internal organs and wine to Ceres.