Draw a picture of yourself with the negative thoughts affecting you (could be a black cloud, or your own interpretation of how they are affecting you).
Charge a red candle with healing energy, light it, and hold the tip of the picture in the flame. After it's lit, drop the picture into the cauldron and let it burn.
Now, with the red candle still burning, draw another picture of yourself without the negativity.
Place this under the red candle and let the candle burn out. You are done.