4. Earn a living, but not by writing.David Seidler: A trust fund is a valuable writing tool, but if you do have to earn a living, try not to do it by using up your writing energy. Avoid at all costs working in advertising, journalism, teaching, reading other people’s dreadful scripts. You only have so much creative energy in your soul each day, and if you use it up earning a living, when you get home and say, “Right, after dinner, I’m going to do my two hours on my script,” you’re not going to work two hours on your script. You’re going to watch television and drink a beer. Learn a craft. Become a plumber. Make a shoe. You’ll be so bored doing it, you’ll go the extra mile to get your writing done and become successful.
Source: Indiewire Screenwriting Tips | Indiewire
Good Advice. Special mention no 4.