consistency and discipline are what you should have first. if you can't handle doing the same thing every day, there's no way you can hope to reach decent productivity levels.
of course, there are ways to help with that. many people have different approaches, but this is how I do for mine:
1. Plan a roadmap. Not necessarily a hyper-detailed plotline, but a chart of plot points and locations. You jot down the aim for one particular chapter, write down the locations you're gonna visit, and have a bullet point of what you want your chapter to establish, reinforce, or achieve. Most web authors end up with hiatuses and blocks BECAUSE they don't have a plan for their stories. Not saying planning is crucial, but when you're stuck on a rut with no idea how to write, having a pre-planned roadmap helps with that a lot.
2. Write rudimentary. Don't go for sweeping sentences or intricate proses for your first draft. Go elementary. Go ham on repeated words. Your first draft is supposed to be the base of your chapter. You can leave the editing for later. Personally, I build the base as I edit, but that's because I already know what I'm gonna write, so might as well spice it up as I go. If you aren't used to the process, just go for easy words. Instead of A glint of passion shining in her pupils as she laid a longing gaze at me, you can opt for a She looked at me lovingly first. When you're out of your temporary rut, go back and spruce things up.
3. Do it every day. This isn't hyperbole. Literally, do it every day. Sit yourself down and try to hit a certain milestone, be it 100 words a day or one scene a day. Personally, I go for at least 500-600 words a day. I've been doing it for a consistent month. As for you? Start today. Right now. No excuses. You got time to read manga or jack off? Write. Taking a shit? Bring your phone with you on the throne and write. No computer around you? Get a paper and a pencil and make your draft. Depending on how much you value your craft, dedicate at least 30 minutes or an hour of your day JUST to write. You want to hammer that practice deep into your skull until doing it feels like second nature. That's how most professionals get by.
but what do i know? I'm just some guy on the internet who loves nipples and sucks off dogs, do take my advice with the biggest grain of salt you could find.