It sounds so simple but is really profound. We often sell ourselves short. Building up your emotional strength so that you can both control it and harness the strength it can give you, rather than being held sway by emotional outbursts.
Be positive, optimistic, think positively. Find something good in everything you have, you do, you hear. And find three good things about every person you meet. Meaning, do not hate people. Hatred is weakness. You don’t have to love, just don’t hate and always seek the goodness in others.
Only you can build your self-confidence. Believe deeply in yourself because that’s the first step. But even when you don’t feel so confident, at least do your best to portray confidence. This is a booster in itself and it is important that you keep it up.