Don't give 100 percent to your day job
Lots of established writers give this piece of advice to young writers: keep your day job. I think this is good advice, but it needs a caveat. If you are a writer with a day job, you should not expect to be great at that day job. There will always be a little piece of you that doesn't want to be where you are, that would rather be taking notes and reading books and reorganizing your draft and fleshing out your characters. You will need to reserve time and energy for that part of yourself, and thus will be unable to give 100% to your day job. Don't expect to perform at the level of your coworkers who are not using their job to subsidize their blissfully unprofitable vocation.