The key thing is to retain the person's attention and interest during a trial lesson. Dragging them into the briefing room is one quick way of loosing their attention and interest. Keep it simple and straight forward!
I normally meet them and ask if they would like to go anywhere in particular and then head out to the aircraft. Usual safety/hosekeeping points are mentioned and then show them the control column and rudder pedals and which control surfaces they move, by showing them out the window.
Start up and get into the air. In the cruise show them the attitude outside for straight and level flight and advise them to look outside and not stare at the instruments. Show what happens to the horizon when you pitch up and down. Then get them to play with the controls and then show the rudder and lastly the trim wheel (if they have got the capacity!).
Might then show the ASI, Altimeter, DI and the RPM gauge and normally state what altitude we should be at or not above.
Then let them lfy it for the rest of the trip and I sit back and enjoy the view out of the window!