Decrees are a wonderful way to re-program your mind, helps prevent negative thoughts from manifesting. Whenever you find your self entertaining negative thoughts and ideas say a decree. One example is
"I Am God in action in me now"
Or another simple one is
"I Am a being of Violet fire, I Am the purity God desires"
And another more complex
"I Am whole, perfect, strong, powerful, loving, harmonious, prosperous and happy"
Doesn't matter what you say, as long as it is an affirmation of who you are; the divine manifest in human form.
"I Am a radiant being of light"
The universe has to re-arrange itself to manifest your command. Don't just let your subconscious mind drag you like a leaf in the wind, manifesting all sort of negativity created by your negative thought patterns. Override destructive thoughts with a powerful decree.
So mote be!