There is always a debate about whether daily affirmations work - the kind of uplifting statements you repeat to yourself in the mirror each morning.
I find a more effective way to improve your mood and self-esteem is to create your own positive scripts for regular re-reading and study. On those days when you're really down on yourself and think that you're a failure, immersing yourself in a book crammed with notes about your qualities and accomplishments can restore your balance, brighten your spirits, and re-energize you for the rigors of the job hunt.
Keep a notebook close by and jot down every little success you've ever had. List your personal characteristics, work and non-work successes, little things you've done that made you feel proud. Record what other people have said to you as compliments or in gratitude. Note any awards or trophies you've ever won.
Describe your accomplishments, big and small: completing a difficult class, learning how to bowl or play a decent round of golf, teaching your teenager how to drive a stick shift, losing that last 10 pounds. No one reaches adulthood without a long string of successes along the way but we tend to discount them because our emotions are engaged by our failures, the "ones who got away."
Keep adding to your book of positives as you think of more and more accomplishments (the list will grow, the more you think about it). On the days when you think your value to the world is zero, take out your book to remind yourself of your own worth. The world is a better place due to all of our collective efforts so give yourself an emotional pat on the back.