1) They were committed to the teaching of the Apostles. This is a challenge to those who are given the responsibility to teach the Word. What are we giving out that is worthy of someone being devoted to. It has to be so much more than stories and feel good sermons that do very little to create a workable faith that sustains during the week. It has to be sermons that create an "awe" in those believers who listen intently and are committed to sitting under our spiritual teaching. This is a task that is so deeply important to the spiritual growth of the believers in our churches.
2) They were devoted to the fellowship. This is an area that I think we have missed. We have tried to convince people for years that their "church attendance" is what God uses to measure their devotion to Him. The Bible tells us that they were devoted to the fellowship, the body, not he building. How many Christians come to church and totally miss this because they have fulfilled the job of church attendance but are not devoted to the body. Devotion to the body means that we do everything within our power to make sure the body is healthy and maturing. There are a lot of ways that we assemble as believers that shows our devotion to the body but wherever it is it must bring life to the fellowship not harm.
3) They were also devoted to relationships with one another outside the walls of the church. Christians lived with a sense of community that involved communal living which involved confession and Lord's Supper together. Real Christianity involves getting involved in the spiritual development of one another.
4) Finally they prayed together. When we pray with and for one another together, it just does something healthy for the body. Obviously when the church lived this way people came to Christ. We need more of that.
The rest of that passage really gives great insight into the results of Christians who live for God and are devoted to the things that please God, not the things that please us.
A church that lives together in community and devotion is a church that will stay together and impact the world for the sake to the Kingdom.