Here are some metaphors from articles, music, and literature:
1. The O.J. Simpson courtroom had become a war zone, with witnesses caught in the crossfire.
Target: Simpson courtroom
Source: a war
Ground: extremely active, volatile, both have a "battle" going on
Tension: war has bloodshed, death and little order while courtroom usually has a little order to it
This statement makes the scene seem very fiery and that conflict and disagreement were raging in the courtroom. It shows how tempers flared and things probably got disorderly. It makes the scene seem more frenzied and hectic.
2. A "couch potato"
Target: lazy person
Source: a spud
Ground: docile, dull, lifeless
Tension: a potato is a vegetable that eventually is put to productive use while a lazy bum is just a human on auto pilot.
This aesthetically gives you the vision of a no-good, lifeless slob. It paints the picture of a fat man with his hairy belly showing, chip crumbs in the crevices of his man boobs and a blue glow lighting him from the television.
3. The World is a Gutter (Enuff Z'nuff, 1991)
Source: sewage system
Ground: poor conditions, stingy, gutters are full of "crooks" (rats)
Tension: there are some actual pleasant places in society
This gives the post-apocalyptic feel of a Kurt Vonnegut novel minus the humor. You picture the slums of a 60 Minutes special, the scenes from COPS, and the children from those Feed the World commercials.
4. The rain came down in long knitting needles.
Source: knitting needles
Ground: thin, sharp
Tension: knitting needles are solid, raindrops are liquid, rain can't hurt you (in individual doses) like a needle's prick
This makes the rain seem more angelic, almost like ballet dancers landing from a jump except these drops probably have a sting to them as rain sometimes does as it hits you.
5. Time is money.
Ground: valuable, precious
Tension: One holds material value while other is valuable towards tasks and a higher purpose. Money is alos tangible while time isn't.
This makes the value of our time relatable to something we actual put value in: money. It conceptually makes our time on earth more precious and makes us want more.