Hey Fro, I was in your boat many months ago, so maybe my experience will help you.
I made a commitment to riding at least 3 times a week. First, I rode about three miles, all road, mostly uphill one way. Then, I increased it to 4.5 miles uphill one way (note: this mileage is one way). Then, I added more mileage. I was always pushing myself to ride a little bit faster. I had ridden with Epic Mountain Biker and I knew I had to push it if I didn't want to be a total burden to ride with. So, I would ride a regular route and see if I was doing it faster. Then, I increased the mileage. I got to where I was doing about 12-14 miles in an hour (again, all road). I would then try to mix in the trail rides on the weekends.
I'm still slow, but I'm faster than I was. And, stronger. I can handle climbs better. I huff and puff but my breathing recovers faster now, too. I can keep going where I used to have to quit. But, I'm far from being as strong as I want to be. Epic, Dirttorpedo, Pain Freak, they all still wipe the floor with me if they want. So, I gotta keep riding.
Bottom line, consistency. I didn't really start improving until I rode regularly, about three times a week. And, if it doesn't feel like you're gonna die, then you're not getting better.
I read a great book called "
Ultramarathon Man" by
Dean Karnazes which has given me a little inspiration, too. I think it's ShinKen that has the sig that reads something about pain being the weakness leaving your body, which Dean says. You might check it out. The paperback has a section on nutrition which I found informative. The website has a little information, but the book is better.