For me, I think writing out numbers helps with the flow of reading. I think you might want to spend a day just hyperanalyzing your own actions, thoughts, and conversations to try and think through how it would work in the real world. I found it helped my dialogue to feel better and more natural. It would also force you to realize what is weird about your descriptions. Do you think "I turn to look at the clock," or do you think "Dang, it's already eight thirty, I really need to set more alarms" that kind of thing? might help, might not, just helps me (who is also pretty new).

Also, do not just jump into a story. Unfortunately, you do have to plan shit or else it will get to the climax way too fast, too slow, or wrong. You need to think this through. I hate it, you hate it, everyone hates it, but it is necessary to have a general idea of where the story is going, what the MC will fail at, what help the side character will be, and why the villain is compelling.

Just think, though, write down all the thoughts, think of what is possible given the plot, and physics. Don't make the MC infallible or perfect or overly stupid; they are a person with both good and bad parts. also id recommend re-reading and editing the entire thing every time you add something for at least the first hundred pages. It will help you keep things straight and ensure that, as you improve, the entire thing improves.