Moisture
Since you’re new to the world of mountain bikeing, and riding a suitably vintage steed, get a copy of
Mountain Bike! by William “don’t call me Bill” Nealy (1st ed. 1992) it’s a great guide to bike handling skills, and a really fun read.
It’s been my bike-handling bible since back in the day, and good skills are one of those things you can carry from bike to bike regardless of where and what you’re riding.