Ben, from Omaha, Nebraska wrote, “I want to write books the way you do. I find your characters interesting. How do I make readers care about the characters I invent?”
I am not sure there is one way to do this. Moreover, I suspect different writers would answer this interesting question in many ways.
For myself, I would suggest that the writer has to create a character that is—to use Hemingway’s term—true. That is, the character has to be believable enough so that the reader can see and feel what the character is experiencing and connect that experience to the reader’s experience. Yes, more often than not, the writer invents a character, but very quickly, the writer must react to that character as someone beyond invention, as someone with a reality of their own. In other words, the character must become independent of the writer, and the writer must see that character and be honest about him or her.
Still, the writer is inventing a story, thus clearly manipulating what happens. The balance between that manipulation and writing what is true is one of the most difficult aspects of writing.