Be a bitch. As funny as that sounds.
But a GOOD one.
I really am not an expert on this topic, but what I think we should all do is to know who we are, how much we are worth, and gain our confidence from there. And be optimistic - there is always a gret chance for a good ending in this world. Once you are not afraid of the world, you will be on the right path. Try more things that you may like in life, and talk to more people and make more friends. It is also helpful to have really good friends who can share intimate thoughts and go through things with you, so that you can take things confidently and come out more confident of yourself after things. I don't believe in the 'just toughen up' approach - strength doesn't come from becoming impermeable, insensitive and repressed - it comes from confidence and the good experiences that comes from it.
I hope that was helpful.
Love, Tara xoxo