First off, simple is best. Use simple tools. This is a really personal habit of mine, and my intent is not to start a holy war among word processing apps, but I've tried them all and have settled on the basic-is-best app that comes with every Apple; Pages. That's it. It has just enough features and nothing more, letting me focus on the story and not managing macros or a Microsoft 365 account. I also like the essential built-in Dictionary and Reminders apps. My second choice is Google Docs, with the advantage that as a cloud service, I can open my story on my phone and quickly add more text or a comment about something I had thought of.
Use a reminder or notes tool. Siri or Hey Google with the Reminders or Notes app are perfect. Whenever I get a notion, no matter how weird or random, I lift my phone or watch and say Hey Siri, remind me that Maslow's hierarchy of needs is interesting in theory, but it's mostly nonsense. The principle for this rule is: if a thought strikes your fancy, you must record it on the spot. Do not judge yourself or hesitate. (Street photographers know this rule.) Siri or Hey Google makes this habit incredibly effortless, especially while driving. It'll save your thought on your default Reminders or Notes app, which you can sort through later.
Do not look at social media. Social media is explicitly designed to make you feel like your life is being wasted. It doesn't matter how successful you are—there will always be someone out there doing something more impressive that will smite you with sheer envy and impostor syndrome every time. Try going for an hour without checking Instatwittertok. Then try a whole day. Then an entire week. It's absolutely liberating and will protect the precious, foolish self-delusion that is crucial for any serious artist (I mean that unironically!). Also, very importantly, you will miss nothing.
Celebrate every writing milestone. If you finish a page, get up and give yourself a cookie. A chapter? Buy yourself a frilly drink. If you reach the end of act one, go out to dinner. The entire first draft? Take a short holiday. It took me forever to realize that I was also my own boss as a writer. What kind of boss did I want to be? The mean boss who took achievements for granted? Or the cool boss who threw morale-boosting office parties? Be the cool boss.
Write in the mornings if you can. Your creative mind is fresher then. I know some people can write at night, but I think most people start the day strong and end slightly flat. When you get home from work or school, you need to delineate a clear physical break to prepare your mind for creative work. Simple, no-frills meditation and floor exercises can give you that in a short time. I'll meditate for ten minutes and do basic stretching stuff for fifteen minutes, and then it's like I'm a different person. Otherwise, you risk trying to write with a cluttered mind, and that's just like fighting a dang land war in Asia (which Princess Bride fans will know is one of the classic blunders.)
Minimize digital distractions. Do not mentally consume anything that doesn't expand your knowledge and make you think. If you're reading a bad book, I now give you permission to put it down and never look at it again. The same goes for TV and movies—if what you're watching absolutely sucks like a lemon, I implore you to stop watching immediately. Don't worry about the money you spent on those things. Everything you consume influences you as an artist, so if you continue to watch Moonfall (oof) out of guilt for that $3.99 rental fee, your limpid pool of creative acumen will become polluted with little particles of insignificance. Spend time instead on the good stuff and the good stuff only. Your time off from writing is meant to inspire and refill your creative well so that you can keep going on your long-haul journey. Be brutally shrewd with the time you spend in media.
Write in short bursts. Write for twenty minutes, then get up and move around for five. I'm a big fan of the Pomodoro productivity method, where you work for short stretches and take regular mini-breaks. Practically anyone can maintain focus for twenty minutes, especially with the reward of a five-minute break at the end. I like to use those five work-free minutes to walk around the backyard or do a few more stretches. It feels downright luxurious and maintains mental stamina.
Get lots of sleep. What's that old rule? Eight hours of work, eight hours of sleep, eight hours of what you will? Whoever came up with that was on the right track. Try to honor that as much as you can, even if it makes you feel silly and lame going to bed early on a Thursday night. Sleep is pure creativity fuel. Kids know this instinctively.
Find a fun hobby totally unrelated to writing. There are no goals or deadlines for these endeavors, which is essential. They are pure-play and necessary to let the mind wander and relax. They're also great places to find unexpected inspiration of the non-verbal, non-narrative kind, like the beauty of a flat 9 chord. Life is not entirely about words.
The cumulative effect of all these simple habits is to blend writing into the daily fabric of your life, like exercise, watching TV, or Taco Tuesdays. When sitting down to write becomes routine, it feels like less of a big deal. And that's incredibly important. In my experience, writing doesn't respond well to really hard, intense work sessions. Fatigue sets in. The brain overheats and dries up your creative mojo—that mysterious liquid, variable in its viscosity, non-Newtonian. The harder you hit it, the more it resists.