The Art of Love by Philaenis of Samos is the first sex guide we know about. It was written probably around the third century BC and therefore was likely missing the all important chapters on handjobs on ferris wheels that modern guides swear by. The author, one of the few women to ever tackle the subject way back when, is believed to be a courtesan, which was the fancy word people used for hooker in polite company.
Evidence of the manual was found in the Oxyrhynchus papyri, a pile of papers found in an ancient garbage dump in Egypt. Only bits and pieces survived but it did inspire the poet Ovid to write his dirty story of the same name later in history, so it must have been pretty awesome. Either that or, since no other sex guides seem to have ever existed before, it was cool the same way that the bra section of the Sears catalog is hot reading material for boys when they're 13.
Actual Art of Love excerpt, (probably).
The book went through a methodical approach to sex, kind of like a how-to book for our primitive, Cosmo-deprived ancestors, including a listing of positions, aphrodisiacs, how to pick up the ladies, how to kiss and a portion on cosmetics, presumably offering fun ways to trim your pubes so they resemble laurel crowns or chariot racers. Unfortunately, there's no record as to whether or not it included chapters on The Stranger and The Backhand. Many of the papers it was found with include early religious texts, so we're guessing the priests and nuns got to them first.