The most important tip he gave me was riding out of the saddle. XC you tend to ride in the saddle on descents, because you keep the saddle high for good pedalling position for the climbs. On the next technical descent you face, lower your saddle all the way (bring an allen key if you don't have a QR), then ride the entire section off the saddle.
The lesson here is that you use your legs for suspension. Even when I am riding an 8 inch travel bike, I still depend on my legs to smooth the ride and control my bike.
First practice riding out of the saddle on a smooth descent. Crank arms should be level (as opposed to one foot down and the other up). With you legs almost fully extended, you should feel balanced on your bike or slightly rearward (if you feel like you are leaning forward, lean back).
After you feel comfortable like this, then descend down that tough section. Use your knees and thighs as your shock absorbers. If it gets steep, lean back and down with your butt over the rear wheel. If you have to go over a drop, like a water bar or a ledge, do the same thing.
The one area I have improved using this method is a sharp but small dip in the trail, like into a stream bed. While standing on the pedals, I let my bike dip down the drop then back up the climb without losing momentum or control. It is like I am standing straight but the bike is doing the up and down.