Lisajane,
This will be different for everyone. Practice makes perfect so keep at it.
I would also invite you to take a look at this thread.
http://sg.paniccenter.net/support/viewmessages.aspx?forum=30&topic=53677&ForumName=Challenging%20Your%20Anxious%20Thoughts&TopicTitle=Helpful%20Questions%20For%20Challenging%20Your%20Anxious%20Thoughts
It deals with this very same subject and has a lot of great tips!
Danielle, Bilingual Support Specialist
My worst thought is "I'll never get better". I have it all day everyday. Can you guys give me some thoughts to challenge this with. I believe it so much that I am not able to come up with challenging thoughts. Also, how long has anyone noticed when they have begun to challenge the negative thoughts that you see improvement? Thank you for any help and advice.