Do you realize your mind is always filled with one thought or another? Keep a supply of positive thoughts on hand, ready and waiting for you to focus upon when your negative thoughts fill your mind.
Understand fighting against a negative thought will not rid you of it. In fact, the energy you set against that negative thought will make it more intense. How? You start to dwell on it even more.
Beginning today rather than rejecting your negative thoughts, replace them with positive, creative, and constructive thoughts. How? Crowd them out by keeping the mind busy with uplifting endeavors.