I think time helps. For instance, I was a very insecure teenager but then who isn't at that age? The older I get, the less ****s I give. I don't care so much about people liking me and frankly it's impossible: as a woman the moment you open your mouth you'll get criticized so who cares. I say what I want to say (not at work though, I still need to pay my bills) and go on with my life. If people don't like it, meh. I also have found that trying new things can improve your self-confidence: a new hobby that you discover you're good at, a new sport, etc. Even things that scare you where you think "I'll never be able to do that" you still do it and you find out "hey it wasn't so bad after all!" can improve your self-confidence because then it's like "I'm unstoppable!"