I don’t really have a lot of writerly advice. Mostly, in order to be a writer, you just write. Write when your writing is shitty. Write when it’s not. Just write. And when you aren’t writing, read.
But the real, practical advice I would give is this–go get rejected. A hundred times. A thousand times. Go get rejected until you can absorb the blow of it. Think of yourself as one of those old-timey guys whose job it is to get hit in the stomach by a cannon ball. No matter what, it’s going to suck, but the sooner you acquire the skills to absorb the blow, the better.
I’m not there yet, myself. But I see it as a necessary place to be.