We have a useful item in the Podcasts/Resources section of our site.  It is helpful material on how to approach personal witnessing.  Here is an extract:

“Speak to convince the mind first. Paul “entered the synagogue and for three months spoke boldly, reasoning and persuading them about the kingdom of God.” (Acts 19:8): reasoning, as to the mind; persuading, as to the heart. It is of no use urging persons to believe unless they are clear in their minds what they must believe.   When the mind agrees, then we can look for the word to be received into the heart. A careful reading of Jn 3 indicates that the Lord Jesus worked this way with Nicodemus. In verses 1 to 3, they are speaking face to face; verses 3 to 8, mind to mind; from verse 9 onwards heart to heart.”

You can read the whole thing here.