I confess, I have always found this to be Jesus' most perplexing parable. What behavior is commendable? Whom are we to emulate? Who is acting justly? What is the lesson here? How can we apply it to our own lives? Rightly understanding and applying this parable has always been a challenge. While some early commentators followed Origen and tried to establish significance to every detail of the story, Calvin rightly points out, "If we were to attempt to find a meaning for every minute circumstance, we would act absurdly" (Calvin, Commentaries, Harmony of the Gospels). Augustine was one of the first to advocate that what is good and imitable in this parable is the unjust manager's desire to plan ahead. In other words, his shrewdness, which the master commends, lies in that he sought to prepare for his future not the means by which he carried it out.
As far as Jesus' cryptic declaration that we should "make friends for yourselves by means of worldly wealth," many take this as Jesus urging us to do good deeds. With his typical wit and understandable style, Luther explains it like this:
You must hence remember that eternal life consists of two things, faith and what follows faith. If you go and believe and do good to your neighbor, everlasting life must follow, although you never think about it. Just as when you take a good drink, the taste will follow as soon as you drink, even though you do not seek it. So it is also with hell, the damned do not seek it, but it follows unsought and undesired, and he must inherit it whether he will or no...
Should God give us heaven for our works? No, no, he has already given us heaven freely, out of mere mercy. Therefore give unto the poor, in order that the eternal tabernacles may follow, and not that you may merit them by your works.
-- Martin Luther, Sermon for the Ninth Sunday after Trinity, Church Postils.