I have been thinking about these issues a lot over the past two days as I've been pitching various stories, getting on the phone, emailing ideas around etc. But one piece of advice I often think back to is a gem Michael Gubbins (editor of Screen International) said in a talk at the Screenwriters Festival - illustrated below in my own funky style:
The message seems to be -if you want to write for other others, write for yourself. The market wants you to be you. And you'll be more successful. We don't want another same old gangster film, we want City of God - a story only they can tell. Only Scorcese can be Scorcese. And he can do it better than you. So what are your own stories? And why would the world want to see it? Easy! ha ha
Lastly, I would add another one to Michael's three:
If you want it made then go do it.