It is SO important that when you sing you show that you are actually enjoying it. If you are singing a Requiem, you probably won't be grinning but sing it with your eyes. Beauty of the music should show in your face.
When singing something livelier and less serious, smiling is a must as long as it doesn't impede the sound or create broad vowels that can flatten your tone.
I think there are a few ideas that can help you to be certain that the finished product connects with your audience which of course is the bottom line.
- You as the director must have an understanding of the music & the text and how they work together to get the MEANING across. The big job is to be sure that all of your singers are on the same page.
- Once you have decided what the song means, then make certain as you are learning the parts that the PHRASING maintains the story you are trying to tell. Breathing in the wrong place is like putting a comma in the phrase where it doesn't belong. For example, there is huge difference between Let's eat grandpa and Let's eat, Grandpa.
- If you and the singers are enjoying yourselves no matter how serious or fun the song is, your audience will enjoy your presentation.