I think what I would say to my younger self and probably to younger just starting-out writers is that a lot of times you're just afraid to put yourself out there and it's uncomfortable because it's working up the courage to do something to push yourself to do those things.
The only true measure of success is the ratio between what we might have done and what we might have been on the one hand and the thing we have made and the things we have made of ourselves on the other.