I’ve always been someone who lacks good self-esteem. I don’t wear tight fitting clothing. I dress in gym clothes most of the time. In settings where I am not 100% comfortable I often won’t say a word. The one thing I’ve found that helps is the “fake it till’ you make it” mindset.
To me, this mindset means act confident until you really are confident. At first it was hard to act on this mindset instead of just think about it. But once I did, I changed completely.