It's sometimes nice to combine a song with a tune. You'll need a song that you can sing in an appropriate key (G or D mainly if it's in a major key) and a tune in the same sort of meter. I've done a version of 'Spanish Lady' as more of a slow lament (it's an unrequited love song) with bits of the reel 'Christmas Eve' built into it, and then a more up tempo reel at the end.

If the band are used to playing tunes, it would help if they also know how to accompany songs. Many don't! Best of luck with it, and I hope that you all enjoy yourselves - that's what it's all about after all!