The excellent Productive Muslim.com site has an article on combating negative thinking with a Islamic slant:
"To be a productive, dynamic muslim,it is extremely important that we inculcate a mindset of positivity. A mindset of positivity leads to proactivity and eventually leads to creating a productive life. If the mindset of positivity is missing, and we are negative and self loathing, and have no hope, do you ever think we would have the enthusiasm to do things and be productive?
One of the greatest secrets to being a productive person is letting go your negative self-talk and switching to positivity. Behind that door of negativity, there is a brighter, happier, productive life waiting for you."
You can read the full post here.