Here's four bits of brilliant advice for those thinking of making a career as a writer...
1. Write because you want to
Writing is an end in itself. It is not a career, or a living, or a way of getting rich. Look at the numbers. How many people make a decent living out of screenwriting or novel writing for more than a few years? In the UK, at least, we're talking about hundreds, maybe dozens, rather than thousands.
Sure, you could be one of them, but the road that destination is so long and so hard, you have to love writing so much that it was never about the money and always about the work, and the words on the page. Both in scripts and in life, money is a very bad motivation for anything. If you're a writer, money is just one of things you need so that you can write. So focus on the writing, not the money or the career.
2. Writers must have a thick skin
If you want to be a writer, you will spend most of your time having your work criticised and critiqued. It may be notes from producers or execs or editors; it may be feedback from friends, or reviews in newspapers, blogs or on Amazon. If you cannot get used to this, writing is not for you.
That said, if you're immune to all kinds of criticism and advice that's not a good thing either. Listen carefully to notes, advice and reviews, but it will hurt. The only thing that will get you through is a thick skin, and a desire to keep writing (see point 1).
3. Writers must be readers
Read books. Read good writing. Read bad writing. Read fiction. Read non-fiction. Read scripts. Read writers you agree with, writers you can't abide and writers you've never heard of.
To improve as a writer - and you do need to improve as a writer - you need to be curious about writing and the world around you. If you read widely, you'll be more interesting in your content and less derivative in your style. And it's never been easier to get your hands on other people's writing. The written word used to be precious. Not any more. (Make a note of that when considering how easy and cheap it will be to get hold of your work and the impact that will have on your income).
4. Write what you like
There's never been more advice out there on how to be a writer, what to write, how to structure it and what to do with it when it's written. Advice is plentiful. But you must find your own way with your own style and your own angle. You should be writing stuff that only you can write. Write what you know if you like. But write what you love. Write what you want to read or experience.
Listen, learn, and improve, but stick to your guns. And the reason why is very depressing: Failure is almost certain. Whatever you write is so unlikely to be commissioned or published, let alone be a hit or a best seller that it's essential that you fail on your own terms. Don't die in someone else's war. Die fighting for what you want to write. It was never about the money, or acclaim. It's always been about the work. About the words. About the writing.
So if you're a writer, write. Read. Then write some more.