(1) Deliberately do things which feel significant to you, which demand that you stretch yourself a little bit. Start doing this as consistently as you can.
(2) Try to spend more time with people who value the things you do.
(3) Face your fears. A lot of what we call "fear" is just negative programming. People in general aren't all that accurate in determining what is a realistic fear, and what is a self-limiting thought left over from confusing or frightening experiences earlier in our lives.

I have finally realized that self-esteem is created and sustained by doing personally meaningful things in a social environment which validates it. Ask yourself, "Who am I, really? What do I stand for? What is my Best Self, as determined by Me?"