How did the creature first demonstrate ethical behavior from his hovel in Frankenstein?
After being chased by villagers, physically threatened, & after suffering in the elements, the creature finds a small woodshed in which he can hide. While there, he discovers the De Lacey family, the few people with whom he will feel a connection in the story. To him, they are beautiful creatures of grace, & he cannot understand why they are sad. Then he realizes one reason is poverty:
They often, I believe, suffered the pangs of hunger very poignantly, especially the two younger cottagers; for several times they placed food before the old man, when they reserved none for themselves.
This trait of kindness moved me sensibly. I had been accustomed, during the night, to steal a part of their store for my own consumption; but when I found that in doing this I inflicted pain on the cottagers, I abstained, and satisfied myself with berries, nuts, and roots, which I gathered from a neighbouring wood.
Thus he resolves to never steal their food again, even though he had been doing it in order to survive. He decides to go hungry, rather than cut into their meager stores. then he takes it one step further:
I discovered also another means through which I was enabled to assist their labours. I found that the youth spent a great part of each day in collecting wood for the family fire; and, during the night, I often took his tools, the use of which I quickly discovered, and brought home firing sufficient for the consumption of several days.
Thus he begins cutting wood for them as well, shortening their own work day and decreasing the amount of physical labor they must do in order to survive. Of course, the sad irony is that he will never be accepted by them, no matter how much he helps the family. He will always be an outcast. He greatly admires this family, and seeks to emulate them, but he comes to realize his own position as a monster in the eyes of humans. Indeed, this is how he's come to regard himself:
I had admired the perfect forms of my cottagers -- their grace, beauty, and delicate complexions: but how was I terrified, when I viewed myself in a transparent pool! At first I started back, unable to believe that it was indeed I who was reflected in the mirror; and when I became fully convinced that I was in reality the monster that I am, I was filled with the bitterest sensations of despondence and mortification. Alas! I did not yet entirely know the fatal effects of this miserable deformity.
Yet he will discover them soon, when he reveals himself to the family, only to be torn away & cast out into the world once again.
The creature first begins to show a great interest in the humans he is watching. He begins stealing their things, but soon becomes fascinated and seems to care for them. He gathers firewood for them and leaves it at their door. He starts to learn their language and how humans interact with each other. He realizes that he was doing them harm by stealing from them and continues to do work for them when they are not around because he knows it will help them.