Abstain from all appearance of evil

I have learned that a key to true discernment is to abstain from all appearance of evil.  I am not sure what it means as written in God's word however.  I guess it means that if there is something that would cause a believer to engage in sin or to stumble, then one should stay away from it.  I believe it would also mean to guard my heart, and think on things of God.  A Christian is to be grounded in truth, in God's Word and let the Holy Spirit lead the way.  I myself can rest assured that this is true.  That gives me great comfort in knowing that I am not alone.