A friend thinks using Deep Third POV would make for a larger word count, and in some ways she’s correct. But DTPOV does wonders for characterization because it’s like being inside a character’s head and their perception of the world colours everything the reader sees. You then don’t need to describe the character’s personality (words saved right there!) because it’s coming through, in the character's own words, in a painless way.
You do need to know your character well so that you can express his deepest thoughts/reactions. Usually I go back over a chapter more than once, and every time I put in another layer. If the surroundings have changed recently, I let the character describe them. Second time around, I'll see where to deepen the conversation. Third time around and I’ll find I can pin-point a character’s reactions to what’s happening. If you don’t know what they feel first time around, don’t worry. By the third trip, you’ll have it.
Not everyone starts writing with a fully-fledges character in their mind. I certainly don't. They grow with the writing, so if you need to get to the end of the story before you truly know your characters, then don't let it worry you. You can always go back and add stuff later.
Expressing things through a character means you need to keep track of them and their thought processes in your own mind (or a little black book), but it is an easy way of revealing why the character does things. If they like or hate someone, enjoy food, or feel insecure, it can all come out in their internal dialogue. Here’s a little example of my own: the opening paragraph of Treason, currently doing the rounds of agents.
Matho’s hands clenched. Though he’d bathed in a barrel yesterday morning, cut his thick red hair and cleaned his nails on the point of his dagger as would any man of fortune seeking advancement, Sir Thomas’s steady grey gaze unnerved him. Snatching his brown felt cap from his head, he rolled it in his suddenly damp palms, gazed shiftily back at the great man and dipped his head. ‘Sir Thomas.’
‘Good day, Spirston. Come forward.’
Matho pressed his sword flat against his hip to avoid chipping the chair at his side and moved up to the vast desk standing like a challenge across the centre of the room. He wasn’t going to grovel like a dog after scraps even though Sir Thomas wielded power enough to make most low-born men wary.
Pic is of one of the vehicles used to pick up passengers from the railway station on arrival in Zermatt.