I came across this little bit of wisdom via Hacker News:
There’s one trick that everybody who writes sales knows and nobody else seems to know. This trick is so effective that Microsoft Word has it even built in so you can test while you write.
The F-K score.
The Flesch-Kincaid score determines what grade level you are writing. If your score is 10, you are writing at a 10th grade reading level. If your score is 12, you are writing at a 12th grade level. And so on.
As it turns out, I wrote an app for that. The thing it has over Microsoft Word is that it caculates the F-K score continuously in the background. It also has a couple of tools that suggests how you can improve your score.
I had a very specific use case for that app: a project my wife had in her publishing job. It also does vocabulary tracking, which she needed. Now that her project is over, I find it hard to get motivated to update it. It makes virtually no money. Maybe I should add a Post to Web feature and reposition it as Write Sales Copy That Coverts kind of tool.