5. Develop competence
What better way to feel you can accomplish something than actually becoming more competent in doing so? If your lack of confidence right now extends to various realms, then choose one that’s particularly meaningful to you and try to master it. It can be anything, really. From a professional challenge of some sort to speaking in public. Don’t hesitate to ask for help if you need to do so. The more knowledge and experience you gain, the more confident you’ll become. Start acting differently, and you will feel differently.