Why not start off with" Welcome to white knuckle airways...' we always get you down' and then welcome your passenger in business class and then the two in economy" After this then let them know what to do in the event of an emergncy ie how to open the door (show them the two latches and how to operate them).
Normally a mixture of humour and safety info relaxes nervous first time passengers but also shows them what they need to know if you had an engine failure. I normally point out how unlikely it is that anything unusual will happen but that being prepared is a good idea.