Hey, if you're getting 90% and above you're doing someting right!
Writing well is hard work, no doubt about it. One of the biggest things that I see lacking in my students' writing is evidence of clear thinking.
I work with them on the importance developing a good clear thesis statement, outlining and revising their initial drafts.
The author of the editorial you pasted above emphasized all of these things.
Here are a few resources regarding how to craft an effective thesis statment:
Thesis Statements - Writing Center, Univ. of North Carolina
- Purdue OWL: Creating a Thesis Statement
Writing Tips: Thesis Statements (Univ. of Illinois)
Check those out and see if they help.
When you have a good, well-written thesis, you are clearly focused about what you want to say and how you want to say it. Also, it helps you to determine what to put in your paper and what to leave out. Everything must support your thesis or it doesn't belong.
On the other hand, if you have a point that you feel really needs to be in the paper, but it does not strongly relate to your thesis, then maybe your thesis needs reworking.