You want to deepen your POV? “Be the tree.” Immerse yourself in the moment. Understand the character’s backstory and psychological motives and personal identification and current situation. Conjure actions, reactions, and emotions based upon what you know about your character–because by now, you are your character.
Does this sound remotely familiar? It’s called “Method Acting,” and according to Wikipedia, a wide variety of actors still practice it.
Actors are lucky. They only have to learn one character at a time. A good writer needs to do the exact same thing for every character he creates for his story.
Whether you do extensive biographies on each character before you start or just make it up as you go, you need to know your characters well enough to climb into their skins and be them in each of their appearances. Once you learn how to do that, you are no longer “Average Joe/Jane,” but you’re “Emerson Bilks, County Mountie,” “Juliette Lovelace, Princess of the Island of Cala,” “Mike Sparks, WWII Ace.”
What you’re doing is creating a character who is real–not just for the reader, but for yourself, too. You’re creating an opportunity to escape and be someone else for a while. If it helps, keep props around to get you into character, wear a costume, play music appropriate to the era or mood of your WIP, listen to the accent you’re trying to capture and mimic it aloud.
Play-act as your character. You are your character, so how would you react if the ice cream fell off your cone? How would you respond to meeting your favorite actor? Can you catch a football? Do you get lost in a shopping mall? What do you do when your heart is broken? None of this has anything to do with your plot, of course, but it helps you hone in on who your character is.
Spend time being your character–each of your characters–and you’ll find it easier to write from under their skin.