Yeah, it's basically running lottos to amass a stockpile and then when you're caught up on story, using dead time (no events going on) to run free quests which are the best for dropping the mat(s) you want.
You can eventually get to a point where you're pretty good on mats. Unless you're trying to upgrade every Servant you have to 9/9/9 in which case it never ends lol. But if you're fine with leaving lesser used ones at like 4/4/4 or whatever then you can eventually work your way to a position where you can have enough to skill up a Servant at will if you obtain them for the most part.
May you find your book in this place.
Formerly known as xp1337.