You can use a finger, elbow, foot, sheep, cars, or any object to give you a sense of measurement.
Measure.
And,
Measure again.
Come back after a few minutes,
And measure one final time.
Now cut.
It's the same in your design and creative work.
Draw a thumbnail study before you paint.
Measure twice, cut once.
Organize a chapter of your book into bullet points before you begin writing.
Measure twice, cut once.
Group your color palettes and check the color wheel.
Measure twice, cut once.
Whatever you're doing, there is a version of measure twice and cut once.