Systematische Anleitung zum Fantasieren auf dem Pianoforte, Op.200
Carl Czerny was Ludwig van Beethoven's student and in this treatise codifies the improvisation genres of his time, like the prelude, different types of fantasias, variations and more. It has MANY musical examples, which is why it's very accessible.\n\nIt is very piano oriented, so for other instrumentalists it's inspiring, but there is a translation needed if you want it to work on another instrument.\n\nA video about this treatise is in the making.
It seems a translation exists:
Carl Czerny (21 February 1791 – 15 July 1857)
German (English exists see above)
Type of Thing you Learn
Preludes, Fantasia, Potpourri, Variations, Fugue, Capriccio
Beginner, (More) Advanced