I have trouble understanding why "no" is used here instead of "na". For example, on Tofugu they translate きれいな人 as "beautiful person" and きれいのヒント as "beauty hints" or, basically "hints about beauty". In this vein, "futsuu no hon" should mean something like "book about trivia/banality". Still, it is translated as "(an) ordinary book". Is there something special about "futsuu" that makes it behave as such?
Boundary between adjectival nouns (often called na-adjectives) and pure nouns is actually somehow fluent. Some words are used only with な, some words are used only with の, and some words can be used with both of them.
普通 is a noun with two meanings 'commonplace, ordinary' etc., or 'normal, the norm'. Hence to make it an attribute of another noun, you would use the 普通の construction. 奇麗 is and adjectival noun so is conjoined with な to a following noun. Your example of 奇麗のヒント sounds like something from an advertisment for beauty products or the like, and in that kind of context non-standard usages are used for the very purpose of being distinctive. Normally, kirei is turned into a noun by the addition of the -sa prefix, 奇麗さ.