Jean Hannah Edelstein has been posting some great stuff this last month, using a rather natty question and answer stylee. In answer to yesterday's question, 'How do they reach the decision for how much a book deal should be worth?':
... if you are a first-time writer hoping to get your first book published, making lots of money should not be at the forefront of your mind, because you probably won’t. If you do, it will be like winning a lottery with better odds than, say, Euromillions, but still bad odds. It’s cruel! But it’s true! And I do think that more people need to talk about it: the importance of writers keeping their day jobs.
Jean has way more experience in this area than I do, but I know enough to realise that she's spot on. And despite all the current bluster about authors making millions through self-publishing, for the vast majority of writers, the exact same rules apply.
I say concentrate on good writing. Make the best art you can possibly make and enjoy the process and pride of completing. If your work goes on to make you some serious money, then toot toot, hooray and a giant bravo. Just don't be surprised or disappointed if it doesn't happen.
When you're starting out, write because you want to write. Do it because you want to create something that no one else in the whole wide world has created. Let that be your motivation. The rest will take care of itself in good time.