The thing that makes Setting important enough to be a character is the significance of the place and the way authors create a milieu. Here are a couple of examples:
1. Most NYC natives will take guests by the doorway where John Lennon was shot. As a doorway or building it's not particularly significant, until you understand the role it played in pop culture's history.
2. Every town has a similar place – not necessarily where an assassination occurred, but a place where the locals go to make out, break up, or settle a school fight. Like an old playground or abandoned quarry where high school kids go and park and once every so often a dead body is found.
To make the setting a character in your own story, find a place of significance – or some insignificant doorway equivalent that becomes significant because of what happens there.
To flesh out the setting and the character, let the protagonist show how this place matters to him or her. (or as we've learned let other characters tell us their experiences too). Find key elements to spotlight (even if it's how ordinary the place is) and give the reader a real feel by showing the characters' responses.
Now, to kick it into high gear – use that place at least 3-5 times for different purposes throughout the plot line of the novel.
"A place is just a place. It doesn't do anything. Only people do things," Donald Maass, a NY literary agent, said at a recent conference.
Making setting a character isn't about animating it, but rather about weaving it into the reader's experience by giving it history and showing the strong opinions and reactions characters have.
If it matters to the characters, it will matter to your reader! Give it a try.
3333-24 Virginia Beach Blvd., Virginia Beach, VA 23452