The thing is to know the songs and understand them - so there are no iffy lines where you look blank. And then PERFORM them. If you're outdoors you will need a BIG performance - perhaps a costume would help. Unaaccompanied is perfect, cos then you can gesticulate and do funny voices and crouch down whenthe ghost speaks.

To make a song work that they've never heard and grab them with the narrative - you will have to work hard. The other alternative is to have an attention grabber like a bnrilliant harmony singer, a wonderful accompanist, or a stunning looking girl!