The above Tree of Contemplative Practices is one I found on the Contemplative Mind in Society website that Elizabeth Thompson told me about and is used with permission. You can click through and see a larger, easy to read version.
Here's some advice on centering practice from the site:
Common Centering Methods:
* Count numbers, such as counting down from 10 to dissipate anger
* Repeat a word or phrase, such as a prayer or affirmation
* Smile and relaxing your body
* Go for a walk; get out into a different environment
* Close your eyes and breathe deeply
* Concentrate on breathing, such as breathing out for a count of 8 and in for a count of 4
* Count your breaths
* Doodle or write
* Carry or place near yourself a visual reminder to stay centered, such as a quote or image
* Use sound to bring yourself back to your center. Periodically ring a bell, chime, or other gentle reminder.
Persistence is an important aspect of centering practice. Purposefully centering yourself many times throughout the day, even when you are not feeling particularly emotional or in need of centering, will help to deepen your practice.
I agree with the concluding paragraph above about persistence. The regular practice of centering enables us to do it in "emergency" situations. But don't wait for the emergency to learn how!
My favorite centering method, when it's possible to do it, is to go outside and take off my shoes and stand barefoot on the ground so that I have the sense of connecting with the earth. This is particularly effective whenever I'm agitated or frazzled. I just send all that excess energy through my feet and into the earth where it is absorbed and neutralized. Even if it's impossible to go outside for this, I can do it my office and send the agitation through the floor and into the earth. It's a very centering and soothing practice.