Bike handling is a skill you have to practice. I rate it at the same difficulty as skiing, and I know that I benefitted from skiing lessons.
On club rides I have seen tricky stretches of road pose no problem to old hands, even on tandems and with child trailers, but a newbie on a full sus MTB will go flying off the road.
Find a place to practice, an empty parking lot. Lay out some empty drink cans and practice slow cycling, turning sharp corners, emergency stops, and track stands. Other useful techniques are jump turns, bunny hops over potholes and kurbs, countersteering, looking behind, riding one handed.
You should also carry a mental list of troublesome conditions, such as wet leaves (sand, puddles, outside camber, white paint, metal etc etc.)
The book Effective Cycling has all of this stuff in.