Yep, there is. For one, face them directly. Not only will that point your audio straight toward them, but it will also give them the opportunity to see your lips move. Not everyone can read lips, of course, but even just being able to pick up a few movements to fill in the blanks of words they couldn't understand can help.
Also, talk a little bit slower and if you know you're talking to someone who is hard of hearing, go ahead and intentionally raise your voice a bit. You don't need to yell, but you do want to put it out there so they don't have to keep asking you to repeat. This can be embarrassing for them, too, and they may avoid having you repeat and just pretend they understand or heard you instead.