We have a CRF80, CRF100 & CRF150 (2).
I have read through the owner's manual regarding the maintenance needs.
What is the best way to learn the valve clearance adjustments as well as other scheduled items listed in the manual?
If you have a basic understanding of how a 4 stroke motor works and are somewhat mechanically inclined, then you shouldn't have too much trouble with it. I would recommend that you purchase a "Service Manual" for the bike (s) as they give you a lot more information than the owner's manual does. I have a 150 and a 230 and the manuals are remarkably similar, so you may be able to combine your bikes into one or two manuals instead of the three. Make sure you have the necessary tools to accomplish the maintainance that you want to perform and then dive in............
If you have a specific question, this site is extremely helpful and you will probably get more suggestions than you could ever imagine!

These guys & gals are more helpful than any dealer I've ever asked!
Of course if you have riding buddies, they can help too.
Have fun...........