Wow, this is interesting.
Its amazing what saddle time will do for you on the trail.
Dont focus too much on your cadence for the time being. You already have a sound spin and you will naturally become comfortable on the trail with your natural cadence once you have more time on the dirt. Training specificity states that to become good at any activity you need to DO THAT ACTIVITY. Just riding those trails will do wonders for your speed, handling and comfort and skill level.
If you come to an object or section of the trail you arent smooth on, simply stop, go back, and ride it again, a few times, until you are more comfortable with it. This is something you never do on a road bike, but is perfectly acceptable on a mountain bike.
Be patient. You didnt become a great roadie overnight and you wont be an accomplished mountain biker overnight either. But you do have the lungs, legs, and cardi. The rest is skills and specificity. Both are accomplished with repeated efforts.
You can do it.
Some of the above is good advice: "Don't focus too much on your cadence for the time being. You already have a sound spin and you will naturally become comfortable on the trail with your natural cadence once you have more time on the dirt." and "Be patient. You didnt become a great roadie overnight and you wont be an accomplished mountain biker overnight either. But you do have the lungs, legs, and cardi. "
The rest is a little misguided. I may be miss-reading this but it sounds like BikeCoachDave is saying that if you go ride more you will get better. Or the old expression: practice makes perfect. Sadly this isn't true. You must first understand what you are practicing and then practice with quality in mind. Perfect practice makes perfect, practice makes permanent. So if you practice a bad habit you will get really good at the bad habit. Like any other sport mountain biking has "core skills" which are the foundation to good riding technique.
Example: A rider is slow through the corners and is frustrated by this. So the rider decides he must corner faster. So he goes out and enters every turn going faster than he used to but, his times aren't getting any faster. For quite a few years this bothers him but he cannot figure out why despite going faster his times are not getting any faster. Then the rider picks up a good book and learns that exit speed is more important than entrance speed. Reading the book he also learns that sometimes to get good exit speed you must enter some corners slower (than he is currently entering them). He also learns the correct body position and vision techniques and starts cornering "correctly". Now despite going slower on parts of the course (often the entrance to corners) his times are getting faster. Sadly, this rider was me half-way through my pro career. If I knew what I know now when I first turned pro 11 years ago I might have been a contender. So don't make my mistake, learn skills early and reach your potential before you are 39.
What this means is, athletic ability can only take an athlete so far and
if an athlete doesn't have the basics wired they will stop progressing well
before they reach their potential. In ski and snowboard racing the competencies (drills that show if you have a specific skill mastered)
are so important that the US SKI and Snowboard development team chooses
their athletes purely on their mastery of the competencies, not their racing
results. I know many athletes who can ski, snowboard and/or mountain bike
and get down the mountain quickly but, they have bad habits and are surviving
on athletic ability and daring.
Dan Milkman (World Champion Gymnast, coach and author of "The Inner athlete",
"Body Mind Mastery" and The "Peaceful Warrior Series") states, "Athletes'
problems with learning or improving their skills are tied to weak fundamentals.
To raise athletes' potential you need to rebuild their foundation for success".
With this in mind the fastest way to learn to ride trails better is to take a skills lesson/clinic/camp from a competent skills coach. The second fastest way is to get a good book (Mastering Mountain Bike Skills by Lee McCormack and Brain Lopes is an excellent book) on skills and practice the skills taught in the book. This will take a lot longer than taking a camp (because you don't have some one to demonstrate correct technique, answer your questions and help you learn the skills with specific drills). Either way you go about it remember that when learning any new skill quality is MUCH more important than quantity. US Olympic coaches (in gymnastics and Ice Skating) have found that your quality starts to deteriorate after the third attempt at a new skill/trick. Practice in a "safe" non-scary environment like a field or a parking lot. It is very hard to learn on trail because the conditions (trees, roots, rocks, exposure) can put you in a fearful mind state. So learn off the trail and then try to apply what you have learned on the trail.
The first core skill is having fun. When you are having fun you usually smile and/or laugh. Smiling and laughing releases endorphins which relax you and you must be relaxed to ride smoothly.
So take a clinic or pick up a book and enjoy your practice and enjoy watching your skills grow quickly.