I've been giving workshops on writing for a while now, and there are lots of things to think about. I want to help aspiring writers as much as possible, and that includes a bit of inspiration (you can do this), a bit of warning (it isn't easy) and a lot of practical advice from someone who read and rated other people's writing for a very long time. There's no way to tell a person everything he needs to know. A lot of it is picked up from noticing good writing, focusing on your own writing, and practicing. A lot.
One thing that makes the whole process less frustrating, however, is paying attention at the outset to where you're going and what it takes to get there. I know, there are plotters and pantsers, and pantsers don't want to know the speciifics. Still, keeping track of certain things from the start is essential, unless you like ending up with a manuscript full of errors. Keep a list of all characters and what they look like (if it matters). Did you say Bill has green eyes? You may need to reference that later. And by the way, what was his last name again?
At the beginning of a chapter, put the time, as specifically as possible. This helps later in keeping a timeline that is believable. Did those cops really fly from NY to LA and back in six hours?
Setting up the page in a reasonable format makes things easier later as well. Different entities want different formats, but you can reasonably expect that you'll need one-inch margins (turn off widow/orphan control), page breaks at the end of chapters, double spacing throughout, etc.
Finally, know the expectations of the industry. Forty thousand words does not a novel make in most cases, nor do editors want 200,000 -- too expensive to print. They generally don't like first-person novels from newbie writers, so if you choose that mode, it had better be far above average. And if you don't know what voice is, find out and use the knowledge well.
Just a start, but we all have to start or we'll never finish.