Giving the singers visual information
I'm a fan of supplying my choir singers with visual information when possible.
This can come in a number of forms - sol fa hand signs, clear conducting gesture, visual reminders of singing techniques, modelling good alignment, sheet music, even just the lyrics written on a whiteboard...
When I'm at a choir rehearsal I like when the director gives me a visual component to help me learn and sing the music.
Another benefit from the point of view of the director is that you have to answer fewer questions - because the visual info answers it for you. If a singer does ask a question, you can often answer non-verbally by pointing to the sheet music/whiteboard.
In this video, I'm at the Canberra Chordsmen rehearsal venue which has a big projector on the wall. Luxury!
I like to use the projector when I can. It's not situated where I usually like to stand, but for these warm ups I moved myself in front of the projector so that the singers could see both me and the sheet music for It Always Seems To Rain On Choir Night. Sheet music here.
At other rehearsal venues, I bring my own whiteboard and write the round lyrics on it.
If the sheet music is visible, I'll draw the attention of the singers to specific aspects of it. "What's the key signature of this piece?" "What's the time signature of this piece?" "What's the longest rhythm in this piece?" "What it's called when we start with an incomplete bar?" The singers get a chance to demonstrate their knowledge and contribute to the rehearsal.
I usually talk about some vocal technique tips while teaching a round. If I'm using forethought, I'll pair each technique with a non-verbal visual cue as I teach it (i.e. hands on face to remind singers to release jaw/cheek tension). Then, while conducting, I can do the non-verbal cue and remind singers of the technique without needing to speak.