Many will answer this with lots of artsy-fartsy crap.
Writing a novel is a job and needs to be approached that way. If you’re serious about it you need to write on a schedule when you feel like it and when you don’t feel like it…especially when you don’t.
You want to write a 300 page mystery?
This is how:
Three pages or more a day for 100 days.
Leave it alone for a month.
Take another 60-120 days to edit, revise and polish.
Don’t meditate. Don’t wait for the muse. Don’t take a writing class.
Ass on chair, fingers on keyboard. Go.
Not glamorous. It’s work.