I found this here. My two cents below.
"How do you stop your negative thoughts? I have been pondering on this since last night.

I have a client that has gotten off track and is going back into her bad thought habits.

How did this happen? When you try to stop negative thoughts you are focusing on the very thing that you do not want.

You cannot get rid of the negative thoughts if you are concentrating on them. Trying to push them out of your mind, you thinking about the very thing you do not want.

By the Law of Attraction you are attracting the very thing you are thinking about (negative or positive). Just start thinking good thoughts.

You have to think positive on purpose it will not come naturally. You will have to practice this for some time before in will be a natural thing for you.

Be grateful for the thing you have, such as your family, friends, house, car, your job (even if it is not your dream job at this moment). Give thanks for all things. What is your focus?

Don't worry about getting rid of your negative thoughts, if they come your way just plant a positive thought in its place. Good thoughts will transform your life faster into what you want."

I really love this! I found myself yesterday feeling really in the dumps. The boys are sick and I am getting sick and I just can't seem to "close or finish" anything I start. I was dragging and caught myself focusing on the negative things. So I made myself a list.

I put a date on it (12.31.09) and put it like a journal entry of all the blessings I have received and how grateful I am for them, to date. Doing this made me feel much better!

I had to put some effort into. Kim is right, it doesn't just happen.

I believe this is a worthwhile thing to do. Focus on how grateful you are for every single thing.

Enjoy right now!
Cara :)