I grew up with someone who was hard of hearing. My father lost 80% of hearing in one ear and about 20% of hearing in his other ear when he was in his 40s. I also have a friend who started losing her hearing when she was in her mid-30s due to a lifetime of loud rock music. My advice would be to call someone who’s hard of hearing by their name or get their attention with your hand before starting your sentence if they haven’t been looking at you. Also if you are one of those who tend to mumble or speak very fast, you will need to slow down a bit and enunciate your words to help them out. Don’t go “I’m speaking to a moron” speed, just slow down to what is considered an average pace. Practicing patience will also make everything go better. As annoying as it might be to adjust your speech pattern around them I can guarantee you it’s so much more frustrating for the person who can’t hear very well.