I remember reading somewhere that you are the opener. Introduce yourself, tell them about what you do, tell them you will demonstrate, and then do your first effect.
The opener will depend on what kind of mentalism you do, for example, Banachek's opener will differ from Keith Barry's, who will differ greatly from Darren Brown.
They do different types of mentalism, the characters they portray are different and that's what is important to look at.
What type of mentalism interests you?
PK, mind reading...etc
Truest statement thus so far on these forums.