Here's an excellent tip I got from my aunt, the elderly nun.

When dealing with old people, slow down your talk. It's amazing the difference it makes. When I was 45 and my mother was 75, I could see her eyes widen with pleasure when I began to talk, because she knew she would be able to understand what I was saying.

This applies to people with other English dialects, as well. English speakers around the world use different vowels and lingo, and slowing down from the lickety-split we use at home is a good idea.