Precision increases plausibility

You know what connects sentences with characterization?
Precision.  When you're precise in your word choice, we'll believe that you really know this character.

Vague words make us doubt whether this person exists, because if this person listens to "a song," or just picks up "some book" or puts her socks in "a bag", well, maybe someone who uses such generic stuff is generic herself.

You don't have to get too ornate here. Just think. If you're in Paul's POV, and he scrolls down his playlist and chooses "a old goldie song," well, you know, the real Paul would know what song he chose. 
And if Paula puts her socks into a bag, well, it wouldn't even have to be in Paula's POV. Anyone who can see her action can see whether she puts it into "her handbag" or "a plastic bag" or "her suitcase."

And if Mike picks up "a book," he might pick up a paperback or a Bible or road atlas, or a red book or a blue book....

Theresa talked about "spark," and for me part of this is diction-- word choice. You have control here. This doesn't require a huge vocabulary, but rather observation (or invention).  Without this level of precision, prose sounds slack, without tension, without "snap."  With precision, it'll sound like there's a real person there, not just ink on paper.
Alicia