Teach them to wear an apron (plastic not cloth) when working wetside, and teach them to use the towel after dipping hands into wash water before handling anything on dry side. It's also important to teach them not to lean on the sink edge, rather to stand up straight a bit away from the edge. It is a very good idea to avoid chemical exposures, especially to developers as the allergenic responses can build slowly with time.

Use a paper safe that has spring-loaded doors to prevent inadvertant exposures. Teach them to work in complete darkness for loading film onto reels and for tray processing color prints. Teach also proper use of a low-level safelight for B&W printing, e.g. not directly illuminating the developer tray.

No eating and drinking is a hard and fast rule, with the sole exception being of course the glass of scotch that is kept on the shelf just above the sink. You might also want to think about letting them use their iPods in the darkroom after they become more proficient. I favor classical music played through speakers but it keeps my wife awake at night and so have switched to MP3 players and ear-buds. The use of players might be a 'reward' for demonstrating some level of proficiency at developing and printing. Having music in the darkroom makes the time pass much faster and many people find the work much more pleasant.

For timing things I prefer the GraLab timers with large glow-in-the-dark numerals. Just let the thing run and watch the sweep and minute hands to time processing. Setting alarms and waiting to hear them is a real pain, especially when the iPod is running in your ears.