Kinda broad question, since there are degrees of hearing impairment!
I have a high-frequency loss in one ear, so I don't hear women's voices as well as men's (unless it's Bea Arthur), and I lose sibilant sounds--can't tell p from t, d, and can't tell can/can't--so say "cannot."
Don't mumble to yourself! Face the person as much as possible--besides the sound going her way instead of away and echoing, she may be trying to lip-read (but don't exaggerate your mouth movements--just speak normally). Try not to talk from behind the person.
NEVER talk with your mouth full!
If you're asked to repeat, try to say exactly what you just did, rather than rephrasing. (I'm running a slot-machine in my head, spinning dials of rhyming words until I can make a sensible sentence of what I thought you said--if you change the mix of possibilities, I have to start over!)
NEVER say "never mind" or "don't worry about it" on the repeats--that's such a slap in the face!
Also helps if you repeat questions asked by others, since they're not aware of her problem, and often talking behind her.
Watch where you are in relation to fans on equipment--put a fan between me and you, and I'll lose most of whatever you say!
Get an amplifier if possible.
Sit her near the front of the room.
Watch your tendency to wander around--it leads to bad acoustics with your sound coming from different places.
If she has a very severe, or total loss, see about hiring a sign-language interpreter.
Oh, yeah, if she's got hearing aids that help--don't yell! I'm often tempted to leave mine off--if you yell loud enough, I don't need it, but it will overload my ear!
I, for one, appreciate your effort here!!
