There's a writer named Marth Beck who has written several articles on ACT that are quite clear, personal, and accessible. They would be good handouts to give to clients. If you search on Oprah.com , you can find several articles on ACT. Here's one of them and an excerpt below:
MARTHA BECK'S GUIDE TO AVOIDING AVOIDANCE
The Consequences of Willingness
What happens when we're willing to feel bad is that, sure enough, we
often feel bad—but without the stress of futile avoidance. Emotional
discomfort, when accepted, rises, crests, and falls in a series of
waves. Each wave washes parts of us away and deposits treasures we
never imagined. No one would call it easy, but the rhythm of emotional
pain that we learn to tolerate is natural, constructive, and expansive.
It's different from unwilling suffering the way the sting of
disinfectant is different from the sting of decay; the pain leaves you
healthier than it found you.