(Acts 12-28)
Acts tells the story of the beginnings of the church from the ascension of Christ (approx. AD 30?) until Paul's imprisonment in Rome (approx. AD 60?). Even over that relatively brief period of time, there is a tremendous amount of change. To my mind, the biggest of those changes is the shift from the Jews as the primary focus in the early chapters to the Gentiles in the later chapters.
This shift is perhaps most evident with the dispute over circumcision leading to the Jerusalem Council in Ch. 15. In spite of this, the Jews are never completely set aside. This is clearly demonstrated through Paul's custom of always starting out by going to a synagogue whenever he started out in a new town (cf. 13:14, 14:1, 17:1, 18:4, 19, & 19:8). It is also suggested in Ch. 21 through Paul's interaction with the leaders of the church in Jerusalem (many of whom were part of the Jerusalem Council), though this last does raise some interesting questions.
The concern, as expressed by "James and the elders" (21:18) is that Paul's work among the Gentiles has been misunderstood by the Jews who have believed, but are still zealous for the law (v. 20). To remedy the situation, they suggest that Paul should participate in a purification rite along with 4 other men, ostensibly to demonstrate that he still has respect for the law. In following their suggestion, some Jews from Asia cause an uproar in the temple which results in Paul's arrest at the hands of the Romans.
Although the Lord ultimately uses these events to bring Paul to Rome, which had been His determined plan (23:11), it seems to me that the motives behind them were erroneous. This fact alone should caution us against using anything in Acts as prescriptive instead of descriptive (i.e., a command for us to follow as opposed to a mere record of what happened). One thing I think that we can reasonably apply to our own lives is this: even when we mess up, it will not prevent God's will from being accomplished. Because of this, we can feel free to try our best and not be so concerned about success or failure. This doesn't mean we should throw caution to the wind and feel free to be stupid, either; just not to be paralyzed by the idea that we might be wrong. God will work it out around us if need be.