Francois Couperin(1688-1733) was a French Baroque composer, organist and a harpsichordist. His book, The art of playing the Harpsichord, published in 1716, gave guidelines to the keyboard players regarding body posture, hand position, fingerings. He also mentioned some treatments of ornamentations.
The book later was translated into German, English and other languages. I have the version in Couperin's orignal words in French and translated in German and English. This book has 35 pages long but it is informative. I especially like how Couperin used his music as examples to give reasons to his suggestions regarding fingerings and ornamentations. He was an early adopter to legato playing. He used finger substitutions and ornaments to facilate legato playing. The legato approach could explain his suggestion of using all fingers to play the keyboard instead of using three fingers like Girolamo Diruta and other Renaissance and early Baroque composers had advocated.
Here are the videos about Couperin and his book:
and the Cantonese version: