Hawkear,
I do a lot of off-road duathlons and it's definitely a change of pace. It's harder to find a good rythm or pace on the bike, especially on technical trails. Some basic tips I would suggest: pay close attention to your footing and the terrain on the run; wear gloves on the bike; if you aren't a good Mt biker and it's a technical trail, don't clip in!
Good luck,
JDWard