Here is a short audio Q and A from John MacArthur on the importance of sound biblical teaching and doctrine in the life of any Christian who desires to be useful in evangelism.
Here is another short mp3 audio Q and A on ‘What does a person need to believe to be a Christian?’
Here’s one on what to do when a witnessing conversation gets ‘weird’ and goes down a New Age bunny trail. Bring it back to the main issue: Jesus Christ. This is an Apologetics Q and A.
These are from the Grace To You website.