Larry Hurtado, at the university of Edinburgh would probably be your first go-to guy for this question. He blogs here...http://larryhurtado.wordpress.com/ , and there are a lot of his essays available from that site.

There aren't many direct references in primary sources to what a service actually was. The Didache has some details and the Letter of Pliny talks about Christians meeting before dawn and signing hymns and later sharing meals. Justin Martyr gives the most detailed account here...http://www.ccel.org/ccel/schaff/anf01.viii.ii.lxvii.html

I'll cut and paste it...And on the day called Sunday, all who live in cities or in the country gather together to one place, and the memoirs of the apostles or the writings of the prophets are read, as long as time permits; then, when the reader has ceased, the president verbally instructs, and exhorts to the imitation of these good things. Then we all rise together and pray, and, as we before said, when our prayer is ended, bread and wine and water are brought, and the president in like manner offers prayers and thanksgivings, according to his ability, and the people assent, saying Amen; and there is a distribution to each, and a participation of that over which thanks have been given, and to those who are absent a portion is sent by the deacons. And they who are well to do, and willing, give what each thinks fit...

So they met on a sunday, read the "memoirs of the apostles" (historians are almost completely united in thinking this refers to the 4 gospels) or the OT prophets, pray together, listen to a sermon and then likely share the eucharist.Then there was a collection.

Perhaps you could check the Itinerarium of Egeria. She was a pilgrim in the 4th century A.D. who travelled to the Holy Land. She wrote a letter back home about the places she visited and, importantly, about the liturgy of the Church of Jerusalem. Hope it helps!

The earliest accounts are the New Testament and the Didache, also sometimes called The Teachings of the (Twelve) Apostles, which is a brief Greek handbook on pastoral care.

The Didache. The Didache might actually be one of the earliest Christian texts. Scholars disagree, but it may have been written as early as the 60s CE, which would mean it predates most of the New Testament, including at least some of the Gospels and the Book of Revelation. At any rate, it was probably written by 150 CE, so its fairly safe to say that its one of the oldest Christian texts that didn't end up in the bible.

After Constantine halted the persecution of Christians in 313, it became a matter of public concern to decide which books belonged in the bible and which did not. Eusebius, who was bishop of Caesarea (in modern Israel) and a close friend of Constantine, recognized that many Christians had accepted the Didache as canonical, although he himself did not. But regardless of the fact that Christian bishops eventually decided against including the Didache in the bible, it is a very early source on how Christians worshipped, and it was influential for the practice of many Christians for at least two hundred years.

The Didache is a short text which can be found here. Other versions, as well as links to other early Christian documents can be found here. The most relevant passages are chs. 8-10:

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.

Now concerning the Eucharist, give thanks this way. First, concerning the cup:

We thank thee, our Father, for the holy vine of David Thy servant, which You madest known to us through Jesus Thy Servant; to Thee be the glory for ever.

And concerning the broken bread:

We thank Thee, our Father, for the life and knowledge which You madest known to us through Jesus Thy Servant; to Thee be the glory for ever. Even as this broken bread was scattered over the hills, and was gathered together and became one, so let Thy Church be gathered together from the ends of the earth into Thy kingdom; for Thine is the glory and the power through Jesus Christ for ever.

But let no one eat or drink of your Eucharist, unless they have been baptized into the name of the Lord; for concerning this also the Lord has said, "Give not that which is holy to the dogs."

But after you are filled, give thanks this way:

We thank Thee, holy Father, for Thy holy name which You didst cause to tabernacle in our hearts, and for the knowledge and faith and immortality, which You modest known to us through Jesus Thy Servant; to Thee be the glory for ever. Thou, Master almighty, didst create all things for Thy name's sake; You gavest food and drink to men for enjoyment, that they might give thanks to Thee; but to us You didst freely give spiritual food and drink and life eternal through Thy Servant. Before all things we thank Thee that You are mighty; to Thee be the glory for ever. Remember, Lord, Thy Church, to deliver it from all evil and to make it perfect in Thy love, and gather it from the four winds, sanctified for Thy kingdom which Thou have prepared for it; for Thine is the power and the glory for ever. Let grace come, and let this world pass away. Hosanna to the God (Son) of David! If any one is holy, let him come; if any one is not so, let him repent. Maranatha. Amen.

But permit the prophets to make Thanksgiving as much as they desire.

So in brief, the Didache gives us the version of the Our Father (or The Lord's Prayer) as most Christians know it today. It describes a Eucharist (Greek for "thanksgiving") of wine and bread for the baptized. And it outlines a concluding prayer offering thanksgiving and interceding on behalf of the whole Christian community.

The New Testament. The Acts of the Apostles is really book 2 of the Gospel of Luke. It was probably written in the 80s CE. It includes several references to the early Christian liturgy, two of which are highlighted below:

They were continually devoting themselves to the apostles’ teaching and to fellowship, to the breaking of bread and to prayer. (Acts 2:42)

Day by day continuing with one mind in the temple, and breaking bread from house to house, they were taking their meals together with gladness and sincerity of heart, praising God and having favor with all the people. (Acts 2:46-47a)

So according to Acts, there was a daily service consisting of prayer, readings from Scripture or apostolic letters (which could not yet have been considered Scripture, since the New Testament wasn't finished yet), some sort of devotion (which could be an early form of the Apostolic Creed), and a breaking of the bread. It's important to recognize that the early Christians could do some of this in Jewish synagogues (reading Scripture, some prayer) but they had to do some of this in their own homes (reading letters from the apostles, celebrating the Eucharist).

St Paul gives a full description of the Eucharist in 1 Corinthians 11:

For I received from the Lord that which I also delivered to you, that the Lord Jesus in the night in which He was betrayed took bread; and when He had given thanks, He broke it and said, “This is My body, which is for you; do this in remembrance of Me.” In the same way He took the cup also after supper, saying, “This cup is the new covenant in My blood; do this, as often as you drink it, in remembrance of Me.” For as often as you eat this bread and drink the cup, you proclaim the Lord’s death until He comes.

Therefore whoever eats the bread or drinks the cup of the Lord in an unworthy manner, shall be guilty of the body and the blood of the Lord. But a man must examine himself, and in so doing he is to eat of the bread and drink of the cup. ... So then, my brethren, when you come together to eat, wait for one another. If anyone is hungry, let him eat at home, so that you will not come together for judgment. The remaining matters I will arrange when I come. (1 Cor 11:23-28, 33-34)

Here we see a service involving a blessing of bread and wine. Those who participated were encouraged to first undertake an examination of conscience, and they were also encouraged to show a certain bit of modesty and decorum.

You might also look at Matt 26:26-29, Mark 14:22-25, and Luke 22:13-20.