Always face the person when you are talking to them. Most people who are hard of hearing rely on speech-reading to some extent.
Don't bend your head down while you're talking, because then your mouth is hidden. Keep your hands away from your face.
You don't have to talk loudly, or exaggerate the way you speak, but do speak clearly, without mumbling your words. Don't talk too fast.
Higher pitched women's voices are harder to understand; if you have a high voice, lower the pitch of your voice if you can.
Make sure the lighting is adequate, and try not to have bright light behind you when you talk so there is no glare, and your face isn't in shadow.
Background noise is a big problem for people who are hard of hearing and who, therefore, need to work harder following your conversation. Turn down music, turn off TVs and radios.
Hardwood floors, high ceilings, being situated in the center of a large room can all create acoustic problems. Choose a carpeted room and position yourself off to the side, or in a quiet nook.
Visual information helps. Use printed meeting minutes and agendas, flip charts, white boards, and Power Point presentations.
On Sundays offer printed texts of that day's sermon to people who are hard of hearing.
At meetings, it can be very confusing to follow the conversation if more than one person is talking at a time. Try to control multiple people talking at once.
Noise from phones, copy machines etc make it harder to concentrate. Try to schedule meetings and hold conversations in a quiet room, where the door can be closed and people can sit close together.