Close your eyes and pray.
Unlike berms (discussed elsewhere) its hard to think of specific tips apart from you need speed and confidence.
Speed does indeed help you 'float' over roots and rocks.
In Morzine I was taken done some very steep unofficial runs that were completely covered in roots, bear in mind that roots at 90 and 180 degree angles arnt going to do much its only wierd angled ones that can catch you and throw you off.
Perhaps you need a nice steep rooty run to build your confidence.
One thing I do is to unweight my front and put my centre of gravity back somewhat so at least my front wheel is going to hang up on a root and throw me over the handlebars.
Andy