Sometimes I find it helpful to say the serenity prayer. I like to recite it while I'm about to go to sleep. I've know it for a long time, but only recently have I "rediscovered" it and it's power. It seems so relevant for people with anxiety.
"Lord, grant me the serenity to accept the things I cannot change,
the courage to change the things I can,
and the wisdom to know the difference."