Short answer: Establish writing as a habit instead of a single creative endeavor, learn to trust that the process is messy and involves lots of rewriting and revision instead of trying to get it right on the first shot, take whatever logistical steps you need to help you, and if all else fails, kick start your writing with someone else's writing.
Longer answer: First of all, sympathies. Starting can be really hard. Unlike some condescending memes, I don't think writer's block isn't REAL. I just think it is inherently not a creativity problem. It is inherently a psychological problem, usually with wanting to get the writing right without trusting that one will have to go through the lengthy process of rewriting, revision, and editing. Once that process is more fully trusted and the "Make myself be creative" straining (complete with agonized grunting) is replaced with simply sitting down to work and having the words and ideas come in a generous flow, you will probably find that the only problem you ever have is having more ideas than you could ever write down, and having to choose the best of them to work on.
Secondly, the way out is through, but it's kind of a long trip. I wouldn't expect to be spinning around on gentle European alive-with-music hills by this time tomorrow. Entirely new approaches to writing need to be learned, techniques practiced, and habits established. It can take.....well there's no upper limit to how long it can take, but even if you're going pretty fast, it's not likely to happen in less than a couple of months, and probably more like six.
Of course, at any point in this process, if the words are coming, you can go back to what you were doing. The risk is that you'll end up stuck again. By far, the main reason writers get writer's block and sit for hours in front of a blank page is because they are gripped by the overwhelming need to get it RIGHT. They are having trouble thinking of a good first sentence or the perfect thing to happen next. If you go back to what you were doing because you basically thought of something to write, you might end up stuck again at the next place you feel you must get right. What you really want is to learn a whole new approach to writing––one that is habit based instead of goal based. One where the faucet just "turns on" when you want it to.
I will tell you some jump starts though. I'm nothing if not versatile. If you just want a fix for RIGHT NOW, today, try the following:
- Skip ahead. (Start on page 2 or Chapter 2 or whatever. You can come back and write the perfect first sentence.)
- Turn off all your devices and leave them off. (Distraction can keep you from going deep into your creative imagination.)
- Spend a set amount of time NOT writing. (Don't go do anything else, but sit there for a half hour or so and just let your mind wander. Don't end early. No matter how many good ideas come.)
- Try to write BADLY (Quit trying to make it good. Try to make it the worst you can imagine. Self-indulgent. Purple. Hackneyed. Clichéd. Make it the worst.)
- Caffeine. (Look, I know it's not exactly kosher to suggest drugs, but caffeine is a mild stimulant and it can start neurons firing without making you too high to write. It's also a habit-forming drug (as mild as it is), so be fully informed. It's also not going to do much if you're already a six-cups-a-day type. But every once in a while, it can really kick-start a slow session...)
- Pick up a book that is a little like what you want to be writing. Open the book and start writing the words you see. You will want to "take over" with your own words probably within five to ten minutes. (You simply CANNOT write as fast as you think and so your brain is going to be playing with the ideas you're writing and start to come up with thoughts of its own. You've also "ruined" your beautiful blank page, so you might as well just write whatever now. If you end up writing a masterpiece, you'll still have to go edit the beginning [since you didn't write that part and it would be plagiarism], and that may help give you the feeling of freedom enough to write on your own.)
However, if you are more interested in never having writer's block again, and consistently being able to write easily each and every time you come to the page, you may have to invest a little more time in something a bit like a "writing training regimen."
- First you're going to do morning writing. (Get up early if you have to and write in the morning. This is FREEWRITING, so don't work on anything in progress. Write whatEVER comes into your head even if it's about how hard you find it not knowing what to write.)
- The first few days, you will establish a baseline amount for how much you can easily write before the ideas start to peter out and your brain sort of gets tired. Double That Amount. (This time might be 30 minutes or it might be an hour. You want to keep doing this morning writing until that amount pretty much DOUBLES. [So if you find you are able to easily write for 30 minutes when you start before running out of steam, you want to keep doing this morning writing exercise until you can easily write for 60 minutes.] It may feel like you will never get to this point, but it will. This is such a vital part of the process that it is not an exaggeration to tell you to keep writing in the mornings until this happens even if it takes years.)
- Discontinue your morning writing for the next part. You should be almost overflowing with ideas basically all the time and maybe feeling a little "psychically" uncomfortable.
- Now establish an ability to do a floating half hour of writing at ANY time. (This will NOT be easy. Pick a different half-hour slot every day and sit down and write during that half hour AND NO OTHER. You may try to weasel out of the writing for "just today," you may try to shift the slot around because "one half hour is as good as another," or you may want to just do an hour the next day. No matter what, you must do the half hour and at the time you picked.
- At this point, you should be able to draw upon your inner wellspring of creativity any time you sit down. The words will come at your command.
- Do your best to write every day. Or six days a week. Or at least every weekday like a job.
- Establish a daily writing time if there's any way you can. Despite the incredible versatility of being able to sit down and write at any time (especially if you have kids), you will get better, more consistent creativity from your "muse" if you can sit down at the same time every day. You'll start to have ideas FLOWING about fifteen minutes before a "session" starts. Your muse knows it works for you, and not the other way around, and it's bringing you The Good Stuff™.
- In general, read more. I can't underscore enough how much reading (and I mean a LOT) will help keep your creativity tank "topped off" both with ideas for stories and with ideas about how to write them.
Between your quick fixes and your New Habit Regimen™, you should be able to (actually) start writing at any time you want to. And now you can approach the page as a matter of routine and regimen instead of a single act of gotta-get-it-right creativity. Once you have a creative flow that essentially obeys you (you controlling your muse instead of your muse controlling you--if you are okay with that metaphor), your writing sessions will feel much more like sitting down to just do your thing for a few hours (or more).