With your dominant hand write all those nasty things your inner critic hacks away at you.
With your non-dominant hand, tell the inner critic off, tame it, write positive things about yourself.
This exercise allows those racing thoughts to purge out on paper with the hand you usually write with. Forcing yourself to write positive with your other hand, brings out the inner child who does not judge, allows you the time to slow down and concentrate. BRAIN GYM!
All you really need is the courage to be yourself. Your real value is rooted in who you are, not what you do. The only thing you need actually do is express your real self to the world.