You can do it on your daily interaction with your child. Whenever he does good, always acknowledge. If he fails on something, never let him feel that he's worthless and don't put his to shame in front of other people as it will definitely make him feel so degraded.
Napanood ko sa Facebook na mukhang effective, ay yung dad na nakaharap sa salamin with his baby girl and everyday may chant sila na "I am beautiful, I can do this". I think eventually, mag grow ang confidence ng bata and alam niyang blessed din siya :)