- Build voice. If your character were to walk into the room right now, what would he notice? What wouldn't he? How would HE describe it? What does that say about him?
- Keep things fresh. If your character isn't cliche (which he better not be) then the way he views the world won't be either.
- Won't meander. If it doesn't effect your MC or his struggle in some way, it probably shouldn't be in there.
Let's look at an example, shall we?
Suppose we have a... oh I don't know... GHOST. And let's say our ghost is a jealous girlfriend watching her ex go to prom with someone else. Now let's see what happens when he arrives to pick up the new girl. (Off the top of my head so my apologies if it's not perfect)
I watched with baited breath, unsure if I'd be able to stop from interfering as promised. Erik clutched the corsage as he walked in the door. His date made her grand entrance from the living room, stumbling toward him a little, unused to such high heels. She tugged at her black velvet gown, revealing another inch of cleavage. The dim light from the chandelier above cast a romantic glow on the happy couple.
The second the skank walked in the room I knew I'd never be able to keep my promise not to interfere. She might as well have shoved her boobs right in Erik's face. Could she have picked a tighter dress? And those heels - she looked drunk. She couldn't even walk a straight line.
See a difference? Which is better? What else is accomplished through filtering through character?