1. Convert the distances into units Americans can understand.
Tell them what the events were "formerly known as" --- the mile, the 100y dash, etc. If they did track back in the day or never did track, it is better to say, "the quarter mile" and "half mile" than the 400m and 800m. My mom has no idea what a "meter" is.
2. Tell them what a good time is for the event they are watching.
What is the world record? What is the school record? What does it take to win a meet these days. People have no idea if what they are watching is good or not...
3. Know your history and remind them of athletes they've heard of.
If you are watching the 1500m, remind them of Roger Bannister, Jim Ryun, etc. If they are watching the 100m dash remind them about Bolt and Carl Lewis and so on. They should have heard of FloJo and JJK.
4. If you have a good sense of humor, and know the kids, use that.
My kids love the guy in the booth who makes hilarious play-by-play comments. It fits his personality and he is funny. If you can pull that off, go for it. Nobody will get mad if you make the meet more interesting.