What does Frankenstein learn throughout the course of the novel and how do his plans change?

One could argue that Victor Frankenstein has learned nothing from his experiences reanimating dead tissue and creating a living being from which he immediately recoils. Nor did he learn from the tragic death of his young brother. Mary Shelley's Gothic novel presents a fascinating contemplation of the nature of man and the sin of assuming a "god complex." Early in Frankenstein; Or, the Modern Prometheus, Shelley's protagonist regales his host and temporary savior, Robert Walton, with the history of his efforts at creating life. Frankenstein's comments are filled with messianic fervor and only intermittently does he question the wisdom of his endeavors. He is obsessed with both his pursuit of the ability to create life and with his status among other living, thinking beings. As he tells Walton, "A new species would bless me as its creator and source; many happy and excellent natures would owe their being to me."

Frankenstein can be said to have learned from his ill-considered efforts, as he recoils in horror from his creation. He learns later that the creature responds to being rejected by killing Victor's precious younger brother. He quickly learns to regret his experimentation. He remains throughout, however, obtuse. He eventually brings more suffering upon himself and those to whom he is closest, including his friend Henry Clerval and his beloved bride Elizabeth.

Perhaps the best evidence of Frankenstein's failure to learn from his past and from his mistakes is his ill-fated decision to destroy the female he was creating for the "wretch." Having listened to the creature's protracted story of its life, especially his/its experiences with De Lacy and his children, Victor agrees to create a female companion for his initial creation, who promises to live remotely in the countryside far from human civilization. This eminently reasonable decision, however, is followed by Victor's sudden decision to destroy the female—an act that leads directly to Elizabeth's murder. 

In conclusion, Victor Frankenstein makes a series of bad decisions that result in the deaths of his brother, William,  Justine, Henry Clerval, and Elizabeth. It is questionable whether he learned from his mistakes. He did learn, however, not to play God.