i think honesty is always the best policy.  when using something new, i tell the students that it is the first time we are trying it and this seems to release some of the tension that builds in the room (maybe just in me).  if possible, i select a good student who i connect with and have them "guinea pig" for me before actually presenting it to everyone.  i find this enhances the relationship with the student and also gives me a chance to see what glitches we may run into when going live.  and hi michele!! :)