Personally, I feel that those with many years of experience in the complicated sport of autocrossing should strive to pass on what they know to newcomers. It can be a very frustrating sport to break into, as you can make many mistakes without being aware that you're making them. All you know is that you're a lot slower than everyone else, but with no clue how to change that. It's too easy to fall into the trap of "Everyone else must be cheating..."
I start out the day with an instructed walkthrough. Here I am leading a group of about 30 people, explaining the tricky spots and gesticulating wildly.
During the event, I do "Ride and Drive" runs. I ride along with the novice first, spot the places where I think he or she can improve their lines, then talk about it with them after the run, using the course map as a visual guide. Then I switch places with them and drive them through the course at speed, pointing out areas where my line is different than theirs. The most common error I see is early apexing.
This frequently turns out to be a huge help to the novices. I often see them dropping 2 to 4 seconds off of their times on the next runs, as well as making it easier for them to stay on course. Many times, I see novices equalling the times that I set in their cars, which is rewarding for them as well as making it much more likely that they will return for more fun at the next events.