When I was about 9 years old, studying with a teacher who was a very competent pianist known for presenting concerts outdoors by the East River of New York City, I was given the "Fantasie-Impromptu." It would be an understatement to say that this work was far above my head, guaranteed to drown my efforts before I had a chance to fumble through a miasma of notes. In so many words, I was not in any sense ready to learn this composition.
Now as decades have passed, with students of all shapes and sizes having hungered to study the Impromptu because of its flashy shimmer and Romantic sweep, I wouldn't contemplate handing this mountain of a composition to a Beginner or even an Intermediate level student. Perhaps I would consider the romp with an Advanced student who had a solid hands-on knowledge of scales and arpeggios in all keys around the Circle etc. if he/she would agree to a baby step musical approach.
If anyone were to seriously tackle this piece I would recommend, at minimum, hands alone, slow practice because of the formidable challenge in playing triplets against sixteenth notes in rapid tempo.
Therefore, the Video below fleshes out ways to navigate the complex melodic/rhythmic terrain of the Fantasie-Impromptu focusing on the first page:
(Note: In the initial practicing phase I do not add the sustain pedal)
http://www.youtube.com/watch?v=GLQDSiM7YAE