For I give you good doctrine: Do not forsake my law. (Proverbs 4:2)
If there is good doctrine (Sound teaching) then there is obviously bad doctrine. The question is, what is good doctrine? The apostle Paul instructed Titus, "But as for you, speak the things which are proper for sound doctrine." What followed were teachings about living the Christian life: behavior, marriage, youth, working and naturally faith in Christ. Yet I have often found that many who aspire to teach "Doctrine", major in minutia. They strain at gnats (the explicit) and attempt to swallow camels (the implicit). Good doctrine is found in the simplicity of the gospel of Christ not the complexity of sin. Proverbs 18:4 clarifies the difference, "The words of a man's mouth are deep waters; the wellspring of wisdom is a flowing brook." Deep waters are dark and murky. A flowing brook is clear and clean. Here we have the difference between good and bad doctrine. One puffs up, while the other edifies. To which are you aspiring?
 Titus 2:1
 Proverbs 18:4
 1 Corinthians 8:1