I'm in a similar place to you, OP. Although, I think I'm starting to figure out how I need to work.
For ages, I thought the best way to write, especially for myself, was to be an architect about it. I'd spend ages planning out the script, writing pages & pages of ideas, and then welding them together, although I often struggled to figure out the characters very fully (or that's how I felt).
I think it's hard to plan a character too much, because they don't really exist until you've committed to writing them. That's how I feel it works for me, at least.
Anyway, I spent a few years doing that, failing to finish very much except for some bad short screenplays, and a couple pilots that I also wasn't happy with. The features that I'd write would get part of the way into the second act, and fall to pieces. It drove me mad, writing & rewriting so much of the same stuff.
Im currently writing a feature with only a loose idea of how it plays out, and I'm feeling like it's getting there. I'm partway through the second act, and I don't feel the troubles I usually would, and happy to leave rewriting until I'm finished, which I can tell it desperately needs.
So for me, just having a point to aim at is enough to get me rolling. The trouble I am feeling may come about is, I feel more prone to influence. Like if I watch a movie with similarities, I may shift the script to fall in line with that, and so I just hope that I can make the script consistent in tone. I often waver between thinking this is too serious, and this isn't serious enough,for example.
Regardless, I need to watch movies, read stories, similar to what I'm writing, even if it's bad, because it allows me to be more confident in things I initially felt may not work, or make me recognise things that probably won't work.
I often use YouTube to create playlists for what I'm writing. I'll thrown in scenes/trailers I love that has the emotion/sight & sound of what I'm writing. They could be very different films/shows, or even if they're terrible movies/shows, but there's something I recognise in it, that I like, and find inspirational from. I also have a separate playlist just of music that either is what I imagine accompanying it, or that for some reason or another inspires something.
It's important to keep in the habit of writing consistently, and if you've finished for the day, of taking a day off, if an idea strikes you, or you get a little spark of excitement, you've just gotta jump on the computer and write immediately. Too often I let the moment pass, and I regret it, but have never regretted writing when in one of those moments.
Sorry if it's a bit of a ramble, of if there's a bunch of typo's, I'm using my phone.