Lesson 1: When in doubt, fill it out.
No, for real. Some people are minimalists. I love minimalism. I do not love it in doodle-art (sometimes known as zen tangles). This is obviously taken from a page in a notebook, completed over time in meetings and over phone calls. When I didn't like what I was doing or didn't think something looked the way I wanted, I just hid it amid a bunch of other details.
Also, in some mediums, just paint over the darn thing. Erasers are good too.
But I prefer a hundred things to see to one poorly executed one.