Get clear on what you're going to do. Then, commit to doing it. The rest takes care of itself.
First, clarity: "How do I act so well?" Ian McKellen asks in an episode of Extras. "What I do is pretend to be the person I'm portraying in the film or play." The scene is hysterically funny, but having majored in theater, directed a bunch of plays and videos, and worked in theater for a couple of years after college, I can tell you: more ought to heed Sir Ian's elegant advice.
When faced with the challenge of portraying Gandalf in The Lord of the Rings, a character who, unlike McKellen, is a wizard, Sir Ian tackled it head-on: "I imagined what it would be like to be a wizard," McKellen continues, "and then I pretended and acted in that way, on the day. And how did I know what to say? The words were written down for me in a script."
The irony is intended here, but Mamet gives much the same advice in True and False. To act, say the words. Learn them really well first, of course, and then say them. College theater tends in the opposite direction: glance at the script, go on a spirit quest, mark the script up with intricate notations and arcane diagrams, then, maybe, get off-book.
This is madness. Start by memorizing your lines. End by memorizing your lines if you want. Know your lines! Then, at the right points during the performance, say those lines loudly and clearly. Do all that and you'll be ahead of the game.
Is the feat of writing a book any less prone to unnecessary complication? Austin Kleon shared this page from a 1954 Ruth Krauss children's book:
Ruth Krauss knew how to write a book. Here, she's given you everything you need to know in one page. Does it work? It's essentially how I help those clients who struggle with direction. Do they know about fruits? Great. Page one: bananas. Let's go from there. It works.
Once you've got clarity, the only other thing you need is commitment.
During the enormously troubled production of Fitzcarraldo, actor Klaus Kinski threw yet another tantrum and decided to take a boat back to civilization. However, directer Werner Herzog was committed. As Kinski ranted and raved while packing his things, "I told him I had a rifle," Herzog later recalled, "and that he’d only make it as far as the first bend before he had eight bullets in his head—the ninth one would be for me." Kinski finished the film.
Every writer has a Kinski inside of them, a brilliant but brittle talent. The slightest thing goes awry—coffee's cold, too much noise in the background—and off it goes for the boat. To persevere, every writer must cultivate a compensatory Herzog: steely-eyed, Teutonic, unrelenting.
If Herzog isn't your spirit animal, try James Cameron. Before production began on The Abyss, Cameron went to the president of the studio financing the film: "I want you to know one thing—once we embark on this adventure and I start to make this movie, the only way you’ll be able to stop me is to kill me." As the exec later remarked to a New Yorker journalist, “You looked into those eyes and you knew he meant it.”
(I encourage you to read the decade-old profile in light of Avatar's success. A masterclass in perseverance.)
Ferriss, who just launched his first fiction project, asks Rubin for advice. Writing a story a week is adding a large and highly unpredictable amount of work to his week. Some pieces flow easily, but others take fifteen hours or more to complete. How do you make sure the writing gets done alongside everything else in life?
Rubin shoots straight:
You can decide how important it is to you, and if it's really important to you, you can say, I'm going to make a commitment where I'm going to do this even if it takes fifteen hours. You could decide, I'm going to do it every Monday. I'm not going to go to sleep until I have the one for the week. You could do it every day. You could do it as often as you want—if you're willing to make that commitment. It depends on how strong your commitment is. Fifteen hours, out of all the hours of the week regardless of anything else you have to do, if you commit to it, that's absolutely doable, because there's a lot more than fifteen hours in a week...If you think this is a doable amount, commit to it, and just do it.
Clarity and commitment: What are you planning to do? And are you going to do it?