In a nutshell: with practice, you get better at the technical stuff. (Or, for writers-to-be: complete your first book, then get over it.)
Longer explanation: I’ve always maintained you need to get a couple of hundred thousand words out of your system before you’ll get published. As an established novelist, I think it’s great when you get a book finished and in the bag because, when you move on to the next one (in theory and if you’ve been listening to your editor) you become so much better at putting the components of a novel together.
That confidence is hugely reassuring. You enjoy the process a lot more, and that’s where I’m at currently.
I’m not talking about the prose level, though yeah, that can improve too. I’m talking about the other stuff: putting together a plot, knowing how many words it will take you to do so-and-so, which allows you to plan structure with ease. Understanding when is the right time to let the reader know something about events or certain people.
Even by reading criticisms, you can learn to, for example, develop your own characterisation perhaps. Most importantly, if you’re lucky enough to have a good editor, then you begin to realise where you’ve been going wrong. The whole process is there as an education and all of your learnings can be brought to your next project. Sometimes I think I’ll be practicing for decades (if I’m lucky).
Just like you practice musical scales, you improve at the technical stuff, which means it’s easier to orchestrate your novel, but putting down the notes in the right order, to compose a novel, will still be difficult.
One of the things I’ve always observed, with new writers, is a bizarre attachment to their first book. Sure, it’s their baby, but more often than not it’s going to be a stinker. Mine was, and remains unpublished. (Some people might say the later ones are stinkers too.) But what experience has taught me is that the more you write, the more books you have completed, the better you will get at writing them. So once you’ve sent that Magnum Opus off to an agent for consideration, don’t just sit there, get practicing again. Think. Type.
The good parts are yet to happen.