Dr. Richard Miller has written this short Yoga Journal article, Transforming Negative Thoughts Into Positive Thoughts With Meditation, as part of a series of tools to enhance your meditation practice.  He guides you through a meditation for mindfully holding negative ideas then their opposing positive thoughts in your body to feel how those messages inhabit you.  Then you are invited to hold those opposing thoughts simultaneously and feeling the coexistence of those dualities within yourself.  There is also an audio clip if you would rather hear the meditation than read it.  Enjoy!