For Francophones, the hands-down most amazing compendium of advice and textbook on mountain-biking techniques from basics to more advanced (filled with contact-sheet-like arrays of photos) is the book originally entitled VTT : S'initier et progresser when it came out in 2006 and now in its 4th edition (??) (2016) with the title, VTT ; les leçons d'Absalon ; techniques de pilotage, préparation et entraînement, by twice Olympic Gold medalist, 5-time world champion, and 12-time French national champion cross-country and enduro mountain biker Julien Absalon (and his co-authors Stéphanie Cascua and Alain Dalouche).

Learn French if you need to and get your copy now! (from FNAC)