In the case of a super high ceiling,
you actually will get great results in pointing the light straight
up. This will give you a very nice separation between the hair
and the background, and the direct thrust of the light into the
ceiling will light up the background very nicely.
Example Image - ISO 400, 100mm
Lens at f2.0
FOR LOW CEILINGS POINTED
STRAIGHT UP...
You
can also point it straight up, just pull the diffuser tab out
on your flash, if you have one... This will reduce the amount
of lighting going to the ceiling and spread light to the sides.
In this shot, you can see in the mirror how I
sent the light straight up to the ceiling. I did this because
I didn't want too much light to hit the mirror.