Mark Shea has a good piece up at OSV on approaching the election as a Catholic:

Now the happy thing for Catholics is that we belong to a tradition that is 10 times older than the entire history of the United States, and this gives us access to a tradition of social teaching and political thought that we can draw on in order to break out of our cramped politics and try something new.

The Church calls us to "participate fully and creatively in public life", and that means choosing "those people best equipped to help serve the common good."  As Shea explains, 

Concern for the common good, in other words, means that we involve ourselves politically, not merely on Election Day every four years, but in the way in which we think about the human person and his relationship to the state and society all the time. The purpose of the state is to help the human person flourish in freedom so he can do the good he was made to do and grow in love of God and neighbor....A Catholic who seeks the common good over party spirit is beginning the long process of fighting with the weapons of the Holy Spirit instead of the weapons of this world. That’s going positive.

Read the whole thing.