my (opposite) suggestions:
1. worry about what the world needs obsessively, and give it what it wants, not what you want to make. become a machine that takes in needs as raw materials and spits out explicit and actionable solutions that are written down. this tip is by far the most important.
2. if you want success, it means holding back on the full story if your audience doesn't need/want/can't handle the full story. painful, i know. fluff pieces are what works.
3. write at a 7th grade level only if you think the 7th grade students have enough money to make it worth your while. NB: this is about the simplicity of your writing style AND the simplicity of your content. here is a big tip: simple content is the route to success (as the OP author notes indirectly), which should keep most of your mechanics simple.
4. "good writing" is overrated. "good enough" writing is underrated. "bad writing" can very easily be profitable. hasn't someone said this before?
5. often what you write is not something that would be worth your time to read. don't mistake that idea for your writing being worthless. if you yourself wouldn't read it, you already have all of the knowledge and ideas that went into writing it!
6. finding your own voice is not as important as blending in-- this is assuming that you are really chasing "success" and not self-actualization via writing. if you have a radically different perspective, expose it to your reader only in part lest they become confused or reactionary.
7. force yourself to write for 5 minutes per day and live by the maxim that if you write less than 1000 words on the same topic per day you aren't serious about writing. more importantly: force yourself to edit 1000 words per day.
8. your friends and family are not good at telling you where you need to improve. professional editors are, however.
9. you know that little voice in the back of your head that says "well, this sentence that i just wrote is shit, how can i make it better?" find and kill that voice until it's time for editing.
10. writing and editing are two different things. as a writer you need to write first, stop, wait, then return to what you wrote and edit it. potentially a lot.