Sing
a simple song with that note as the keynote. Sing on an
"ooo".
For example, use My Wild Irish Rose.
Every time you come to the keynote be sure it
resonates
exactly the same. (You'll find that some other notes
resonate,
too.) Adjust as necessary. It will be pretty hard
at first.
That's on-pitch singing.
Sing
My
Wild Irish Rose with
the words. Modify your vowels as necessary to get that
ringing
sound on every note. You will probably have to move your
placement forward to have that happen. Almost behind your
front
upper teeth. When you get that sound consistently,
shut off
the water. (You've probably taken too long a shower.)
Retain that feeling of placement, and mouthshape that worked
to
make that sound resonate.
Carry
over that placement and mouth shape into your chorus rehearsal.