One of the best practices you can adopt is to treat all creative as design.

Always define the “problem” you are trying to solve clearly before you get started. That could mean “I need to educate my audience,” or “I want to make my book feel epic.” This will help you make creative decisions that align with your goals, rather than relying solely on what feels right.
Work top-down. Whenever possible, start with an outline, a brainstorm sheet, rough sketches, or even just collecting references... all before you get to putting together any sort of formal creative. This will help save you time developing ideas that aren’t top notch.
Generate more ideas than you need before you select one. The first idea you come up with often can be the right one, but just as often it is not! Forcing yourself outside of the obvious is the best way to come up with crazy new ways of looking at your project.
Go too far, then reel it back. Push the boundaries of your ideas past where you think they should be, then start to push back into where it feels reasonable. You’ll never be able to see what you’re actually capable of until you toe the line, even if it means sometimes that it won’t work out. The benefit is that you’ll come across real breakout successes that you otherwise would never have seen if you played it safe the whole time.
Leave your personal tastes at the door. This is a tough one to swallow for many people, but it’s important to solve your “design problem” logically before you start applying your personal tastes and preferences. That includes color palettes, font choices, writing tone, or even art selection. Organize your process so that you have space for personal expression, but make sure that it comes after the key elements have been solved first!