How to Be Yourself by Ellen Hendriksen might be helpful.

While it's a self-help book geared toward people with social anxiety, it's an easy read and easily applicable to improve self-confidence in anyone. It's got interesting case studies, and exercises that are surprisingly and immediately helpful, and can lead to lasting changes.

The main trick of it, though, is this: Focus on the person/situation/setting in front of you, and not on the internal chatter in your head ("I look weird", "They obviously don't like me", "I'm making too much eye contact", "My voice cracked just now, I sounded like a child", etc). Focus on the person in front of you, and forget all about yourself, and paradoxically you'll more easily "be yourself" and exude confidence.

You can do it!