I ran a 5k in the woods yesterday. Some portions of the course were extended mud puddles, so my socks got a bit muddy.
The tough thing about a trail running is that it really is more hazardous than pavement running. You can slip in the mud, trip on a root, all that kind of thing.
The fun thing about trail running is the challenge and the sense of being out in the great natural unevenness of things.
They say running on uneven surfaces is good for your ankle strength - if you can keep from twisting them.
Here's my number one tip:
Try not to trip.