Aight it depends. You can take an everyday situation and make it big or you can take a more extreme topic like demons or whatever and talk about it. If you're going for depressed do something with suicide. Its real common. Describe every feeling, but do it in a poetic way that makes the reader feel uneasy. Like If I wanna say "I wanna kill myself". I can say "life's worth decreased, I question the need to breath" or yadayada with yo crazzzeh ass.