I think the hardest part of writing is revising. And by that I mean the following: A novelist has to create the piece of marble and then chip away to find the figure in it. ↗
Revising a screenplay is much more frustrating than revising a song because you have to read through the entire work again while you are changing stuff. It is a lot easier to edit a song. ↗
The thing about the 600 words, I mean some day, you can do a very, very, very hard day's work and not write a word, just revising, or you would scribble a few words. ↗
The usual way - through a long series of rejections, revising my manuscripts, and kept trying again and again. Finally I was fortunate enough to find a good agent. ↗