Scripture is Clear, Necessary, and Sufficient.

By Clear, Christians mean that the Bible is written in such a way that its teachings are able to be understood.

Not that it is always immediately understandable, but that with faith, prayer, guidance by the Holy Spirit and some knowledge of the Grammar and Historical context then passages can be understood. 

By Necessity, Christians mean that the Bible is necessary for the knowledge of the gospel, Salvation (or Justification), for maintaining a spiritual life (Sanctification), and for certain knowledge of God's will, but is not necessary for knowing that a god exists or for knowing something about God's character and moral laws (many of those can be found within the God given conscience of Mankind).

By Sufficiency, Christians mean that the Bible contains all the words of God that he intended his people to have at each stage of redemptive history, and that it now contains everything that we need God to tell us for Salvation, for Trusting Him, or for obeying Him. Also this means that any new guidance, doctrine, teaching or "narrative" cannot be blindly accepted and obeyed but must be tested by the truthfulness of Scripture. It also means that nothing is a Sin that is not forbidden by Scripture (like drinking as an example) and to add to Scripture's sin lists is acting like the Pharisees, who broke God's Laws yet held to their own.  It also means there are no new requirements for Salvation that need to be added to Scripture (like gaining 5 pounds or loosing 30 or circumcision or good works).