dom_daqYeah it's obviously all about riding a lot, just like skiing or anything else. Some tips to improve confidence at speed especially is to always keep your eyes down trail. Know what's coming and don't get caught up in the terrain you are on top of. And just stay as light and loose as possible.
Its really similar to skiing IMO. You know how you carve on ice- roll your ankles but keep your upper body over the skis instead of laying way over in the turn? similar to biking you put the bike tires on edge but keep your upper body over the top of that edge as much as possible.
Turn with your hips and shoulders, not with your bars, get used to trying to place your tires into grooved ruts and edges when making a turn.
If you are coming into a turn too fast, brake hard, but as soon as you start to turn let your tires run wide open. Braking pulls you upright, and doesnt allow your tires to grip.
When going over rough stuff at speed, it is exactly like straightlining moguls- stay light and loose and try to skim over the top, but be ready to absorb some heavy impacts.
Also, crashing on a MTB is way more painful and pretty much every crash has repurcussions(broken parts, gashes, generaly getting hurt). Im much more likely to kill myself or have a catastrophic injury while skiing because of the speed and terrain, but nearly every crash ive had biking has at the least resulted in a cut that needed butterflys.
Take it slow, there is no reason why you need to get super rad on a bike immediatly. I know the terrain and speed seem superr mellow compared to what you ski, but you also have far less control. Take it slow, find your tires limits and your own limits in incremental steps.