When I started out, there was no way to learn. You simply had to get in your car and travel somewhere. Then you waited for three to six months to get an appointment, or to get to see a writer you admired, and get some advice from them. But now it's a different world. But then again, every writer is totally different.
Some writers write two songs a day.
They're turning in 150 songs a year, and they get six cut. Some people write twelve songs a year and get six cut. Everyone is different. There is no constant. But even the one who writes twelve and gets six cut is only getting half of his stuff cut.