For me, part of the joy in mountain biking is building the bike itself. From getting the parts right through to the actual assembly. I savour every moment. Except the hand cleaning at the end of each session.
Much of my knowledge about MTB assembly is from a good friend, BC Kelolo. I reached out to him before setting off on my first of many, many adventures and he unreservedly gave me good advices and tips. Over the years, I accumulated some more through my own readings, research, discussion with fellow riders and numerous trips to LBSes.
MTB evolves at a dizzying rate. I personally can't keep up with most of the tech (innovative or equally useless). Unfortunately due to this, there is a very steep learning curve if you're to dip your toe in building/assembling your MTB. So I only keep track with the ones that are particularly suited for my riding, $ and whatever I can easily source locally. There are one or two things that caught my attention, usually those which are practical and interesting to be tried out. And if my wallet could agree with them.
Many good riders I know are also good bike mechanics. The reverse may not be true, though. Anyways, knowing at least the basics about your machine would be good for you as a rider. Trust me on this.
My answer on Quora - How do I build a mountain bike, from just the frame all the way to the trail?
Modern MTB - Spoilt for Choice
BC Kelolo's Anatomi Sebuah Basikal Gunung
My first adventure