Do you mentally add background music when you write?
(...Don't tell me that's just me.)
I'm not talking about a playlist to rock out to while writing, I'm talking about the music that plays in the background of a scene, in your head. (Unless those happen to be the same songs and line up exactly with the scenes as you write them in which case you, my friend, have enviable timing.)
The thing is, background music is important. When watching a video, the background music tells us when to feel sad, or apprehensive, or scared, or happy, or completely and utterly stunned.
(Take a moment to watch those, they took me forever to choose.)
(After you've taken a moment...) See how the music is the cue for the emotion? When done right, music = emotion in videos.
Which is slightly unfortunate when you consider the fact that books don't have background music.
Therefore, I think we have to set our own. This is with tones. Tones and the right adjectives. Is your character depressed? Use depressing adjectives. Have him/her describe the tablecloth as "faded/puke/moldy green" rather than "grass/key-lime/crayon green." That adjective, like the first "duh-nuh" of the Jaws song or the jaunty beat of Hall & Oates, is a cue. A trigger. "The character is depressed. Feel sympathy."
Of course, adjectives can't be the only hint you offer your readers as to your character's mood. That'd be like...the dance routine for the "happy" link combined with the creepy music in the "scared" link. The actions and dialogue have to match up. But I happen to think the descriptive words are akin to the background music in a video. And background music is quite desirable. After all, Calvin (a la Calvin & Hobbes) once said, "I thought my life would seem more interesting with a musical score and a laugh track."