Common ground was the way we were to approach Muslims as we encountered many in Spain, mainly because they spoke English. We had especially prepared brochures and they always let us read a scripture from the Bible or would read it themselves.
There was no fear of reprisals from Muslims out there because it was mainly used the way Church of England use their religion over here. It is a title not a way of life.
When I worked in a leather goods shop I used to get my boss his breakfast during ramadam so the other Muslims wouldn't know he wasn't fasting. What none of the Muslims knew was that none of them were fasting because we used to chat about it whilst waiting in the cafe. It was obviously breakfast for a Muslim because of the tea that went with it. None of us snitched but we did laugh about what hypocrites they all were.
Edited to add. Muslims in UK are scary