Question

what can help to develop confidence

Answer 1

read swami Vivekananda's quotes and life history

Answer 2

In my opinion success brings confidence. Like if u got 1st, 2nd or 3rd position in any competition it will bring u confidence to join again. And u will be confident on yourself that u can do this.
So
1) success
2) positive thinking
3) opportunity
These three helps in developing confidence.