Vorlich -
OK, so you're approaching a rooty section of trail. For the sake of argument, let's say the trail is straight!
The trail will be contouring across the hillside and will have some kind of outslope itself, so one side of the trail will be downhill, the other will be uphill. Even if the trail is completely flat (let's say you live in England or something...
) the roots themselves will have some slope - they'll be higher closer to the tree.
As you approach the section, position yourself on the downhill side (outside) of the trail.
Just before you hit the first root, aim your bike at the uphill (inside) edge of the trail at the far end of the rooty section.
At the same time, unweight the bike (use the first root as a boost if you like). "Float" the bike through the section, ideally not re-weighting it until you reach the far end. This will, of course, depend how fast you're going, how good you are at popping the bike up and how long the section is!
The slight bit of inward steering compensates for the slippiness without being enough to mean you're not hitting the roots straight-on.
If you're not sure what I mean by weighting/unweighting the bike ("pumping the trail"), might be best to get some input from a skills day or a more experienced rider. Not the easiest thing to learn on the web!
EDIT: Top-tip - look at your exit point from the section, not at your front wheel! (Also applies to riding North Shore and riding rails on a snowboard!).