Choose your paper.
Paper is a very tactile substance, and you can use the feel and sound to help get at those subconscious stresses and anxieties. Newsprint has a nice rough feel and smell. Thin papers rip easily. A heavy stationary sheet will take more effort, but may be more satisfying.
You may also want to get a pad of paper to take with you for attacking anxiety on the road.
Next, write or draw words or shapes that represent things you are anxious about.
Some people may want to write out everything that is bothering them, or draw an elaborate picture, others may just want to scribble an expressive blob that represents fear, anger or hate. Attacking anxiety by drawing it first puts some meaning into the paper. It gives you an outlet for turbulence you may feel inside.
Now, rip up that paper.
When you're feeling acute stress, you may want to rip the paper in big, dramatic hunks, grunting as you go. But for anxiety you may want to express control over the problem by tearing it into meticulous, perfect strips. It can be like disassembling the problem. Find a way that suits your mood, and also the situation. (If you're feeling stressed out at work, you may not want to have a loud ripping match in front of your colleagues or boss, for instance.)
Expressive therapies, such as drawing and ripping paper, have been used successfully to relieve stress and anxiety for years by therapists dealing with serious anxiety disorders. It can certainly work for everyday stress too.
The key to attacking anxiety is to symbolize it into something physical, so you can deal with it.