Say what you mean: the power of your words
Every thought has a vibration. When we speak our thoughts we push the vibration into the material realm, causing an even stronger reaction. We are heard and felt, it is a miracle of sensation, that has the possibility to change the world.
Thoughts of beneficence carry a positive vibration. The word love is one of the most felt words in existence, radiating likewise love to those who engross themselves in the feeling. Negative thoughts carry a negative vibration, which is why thoughts of hate and worry usually return the negativity back into the life of the sender.
The same theory applies to spoken word, as is easy to see from typical conversation. When we interact with peaceful, happy intentions, it is returned to us by our conversing partner. When we argue, it is typically reciprocated.
The universe is listening; as everything is, Gd is, and it is always processing and interacting with our thoughts and words, receiving, awarding, and denying us what we desire depending on our behavior. Words in an active voice and present tense are more potent to interacting with the currency of the universe than worry and fear of future or past or would or could. Words with a positive intention are rewarded with action, and negativity is given passivity.
How to begin to change your thoughts:
The opposite game: When you think or say a negative thought, immediately think or say the opposite, to counterbalance and train your mind into the positive.
Breath centering: When thinking negative thoughts, we tend to reel from worry to more severe panic quickly. Coming back to an attention of the breath, while realizing the worrying feeling is inside, and only inside, can distract us and return us to an equilibrium.
Wonder: If breath centering is hard, when having negative thought streams, as soon as possible find another sensation. Whether a soft fabric, a beautiful color, or a favorite song, enter the realm of the present, and give your attention to sensation. Stop the flow of sadness and invite gratitude.