One of the cornerstones of Reformed theology is the belief that good works cannot save you; in fact, they play no role in your salvation. Salvation consists in the forgiveness of sins, which is a completely free and un-prompted gift from God. Zwingli and Calvin agreed with Luther that even those elected by God to receive God's grace could not perform works that merited salvation. The elect remained sinners, even while justified. This is in contrast with the teaching of John Wesley and the Methodists following him (and much of American Protestantism in the wake of Wesley's influence) that works (performed with the help of God's grace) are necessary for salvation, that the elect can lead a life of Christian perfection, and that failure to do so puts one's election at risk. Calvin compares the life of a Christian struggling against sin to a race. One may not expect to win, but one must race well to the very end.
That said, Reformed churches have had high expectations for moral behavior. The elect, freed from anxiety about their own salvation, can devote their attention to helping their fellow humans. They do so because the same work of the Holy Spirit that brought them to believe that their sins had been forgiven continues to work in them to do God's will. They do so because service to fellow humans glorifies God. And they do so because, as they grow in the life of faith they become more Christ-like, and so take on aspects of Jesus such as seeing the image of God in everyone, even enemies, and reaching out to the poor and imprisoned, etc. The German sociologist Max Weber has argued that Calvinists tend to be driven to perform works, not because they think works will save them, but because the ability to perform good works can be seen as a possible indication of God's grace, and a sign that one is among the elect.
Calvin was clear that even those who are not saved can and should have high moral standards. Calvin makes this case as he argues (against those who think that the doctrine of predestination makes God into an unloving tyrant) that God cares for and showers grace on all humans, the saved and the unsaved. On the list of things that God gives even the non-elect is reason to discern the good, and will to follow the good. In other words, the fact that there are well-ordered human societies in which it is possible to live and prosper is the direct result of God's endowing humans, whether saved or not, with a moral sense and the will to obey it; again, it is important to note that for Calvin moral behavior will not get you into heaven. Moral standards are clear, Calvin thinks, simply through the observation of nature (which, like the Bible, Calvin compares to a book written by God in which God's nature and will can be discerned). And since sin has blurred our vision of nature, God has in addition given us scripture (which acts in Calvin's metaphor like a pair of spectacles to sharpen our vision), which clearly outlines what God expects.
The Bible is for Reformed Christians the final authority on moral thought and action. The Bible states clearly (according to Calvin) what God expects of us, that God will forgive us when we fall short (as we always do), and that God will work in us to live up to expectations. The debates in the Reformed tradition about moral principles have been debates about interpretation of the Bible. For a long period in American history there was a fair amount of agreement on moral principles found in the Bible (the obvious exception being whether the Bible allowed or forbade slavery). So, for example, Presbyterians played leadership roles in the temperance movement, prison reform, labor laws, etc.
This general agreement fell apart in the early decades of the 20th century during the modernism controversies. Churches split over whether or not the Bible was compatible with Darwinism, and over historical criticism (the claim that the Bible is best understood as written by various authors for specific audiences in specific historical contexts, rather than as an inerrant message for all the ages). Liberals (modernists who wanted to combine religion with science and historical criticism) tended to read the Bible as having an emphasis on social justice issues. Conservatives tended to read the Bible as focusing on individual moral behavior and the salvation of souls.
These differences on how to interpret the Bible have sometimes led to schisms. For example, the Christian Reformed Church as a denomination tends to be more conservative than other Reformed churches in America. The Presbyterian Church in America split from the Presbyterian Church in the United States in 1973 because it felt the mainline denomination had departed from strict biblical principles. The Evangelical Presbyterian Church developed in 1981 in order to focus anew on the centrality of scripture and the historic confessions of faith.