What really struck me today as I read this is that Jude was not simply giving an appeal to pastors to be careful to teach the right things to their people. As far as I can tell Jude is speaking generally to all Christians. The letter is addressed simply to those who are "called" and are "beloved in God the father and kept for Jesus Christ" (v 1). So everyone claiming the name of Jesus is to contend or fight for the faith. Every Christian, from 8 to 80, is to stand boldly for truth. (But don't forget truth-speaking is always done in love, see Ephesians 4).
What does Jude mean by "the faith"? I'm not certain because I didn't spend a great deal of time on it. However, I am sure he doesn't mean by "faith" simply the kind of faith that saves us. Otherwise he wouldn't have said that he originally wanted to write to them about salvation, but is instead writing to them to contend for the faith (3a). So I think he is probably referring to the things that Christians believe broadly speaking. In other words, the phrase "the faith" alludes to the questions of theology: Who is God? What is he like? Who is Jesus?
Last thing: I think one application from this is that all Christians must know some basic theology, and they should help each other to fight for it. One simple thing to do to think about some basic theology would be to read through a "confession of faith" like the Baptist Faith and Message 2000. Read an article a day and look at some of the verses. Pray that the Holy Spirit will guide you and help you believe God's Word. Or if you have more time on your hands read a book like Concise Theology by J.I. Packer or Systematic Theology by Wayne Grudem. Or a good website with tons of free, helpful stuff is Monergism.com.