Get somewhere quiet.
Remember a time when you beat up on yourself or just felt bad about yourself.
Focus on that inner voice that is criticizing you. Ask these questions:
Where in my head is this voice? (Front, back, center, left, right)
What does it sound like? (Loud, screeching, gravelly, etc")
What does it look like? (Let answers just flow)
Keep in mind that you are to just give a best guess to these questions.
Now that you have identified something about the way you not-resourcefully talk to yourself, change one of the things you noticed.
For instance, if the voice is screeching and high-pitched, change it to the sexiest voice you can imagine. Keep in my Franz Kafka's advice: "There are some things one can only achieve by a deliberate leap in the opposite direction."