Embracing humility is the root solution to confidence in public-speaking because it allows us to be truly ok with making mistakes. Without this ok-ness, we're walking on eggshells all the time, afraid to make mistakes.
Ideally, mistakes should be avoided but not feared... and humility which takes this fear away.
The best way to increase humility is constant self-education on the topic- Here are some good resources on humility:
Read a blogpost about humility