It shouldn't come as a surprise that one of the primary prayers of the early Church was the Our Father.
It was the prayer that Jesus taught them and so they held it in high regard and didn't want to forget it.
According to the Catechism of the Catholic Church, early Christians prayed the Our Father three times a day:
This indivisible gift of the Lord's words and of the Holy Spirit who gives life to them in the hearts of believers has been received and lived by the Church from the beginning. The first communities prayed the Lord's Prayer three times a day, in place of the "Eighteen Benedictions" customary in Jewish piety.
In this paragraph the Catechism cites the Didache, which is an ancient text that many scholars date to the 1st century. It is one of the earliest texts the Church has outside of the four Gospels:
But let not your fasts be with the hypocrites, for they fast on the second and fifth day of the week. Rather, fast on the fourth day and the Preparation (Friday). Do not pray like the hypocrites, but rather as the Lord commanded in His Gospel, like this:
Our Father who art in heaven, hallowed be Thy name. Thy kingdom come. Thy will be done on earth, as it is in heaven. Give us today our daily (needful) bread, and forgive us our debt as we also forgive our debtors. And bring us not into temptation, but deliver us from the evil one (or, evil); for Thine is the power and the glory for ever..
Pray this three times each day.
Eighteen Benedictions
The Catechism also make a reference to the "Eighteen Benedictions" that were said by many Jews at the time. Many still recite these prayers and, according to Dov Bloom, they are recited at morning, noon and night:
We pray the Shacharit (“morning”) prayers in the morning, Minchah (lit. “gift”) in the afternoon and Maariv (from the same root word as erev, “evening”) at night.
Early Christians recited the Our Father in place of the Eighteen Benedictions and would likely pray at morning, noon and night. Many Christians pray the Angelus prayer in this way today.
If you are looking for a daily prayer practice that is simple and resembles that of the early Christians, try praying the Our Father three times a day.