The following are some random thoughts.
1. The importance of tone
The child of a friend of mine was at a mission. It was a fairly old style affair. When he went home he asked his parents, 'why was the speaker so angry with us?' It was all to do with the speaker's tone.
2. The particular to the general
I think that one of the causes of theological error is that we reason from the particular to the general. So someone has an spiritual experience. It is brilliant for them. Then they develop a theology that says that every Christian should experience what they did. However, God is personal and he brings each of us along different paths.
3. Make people want to believe
Some people make a reasonable argument but their attitude makes you want to prove them wrong. Evangelists should present the truth in a winsome way that invites people to further study the evidence.
4. Beware of enthusiasm
Enthusiasm is a good thing. But it is not an entirely reliable indicator of spiritual life. After all the shallow soil produced enthusiasm, but it did not last. Often churches are most impressed by those who have most energy. But look instead for character. After all Jesus said that love is measured by obedience, not just keenness.