What makes the following sentence difficult to read?
The proposal that the best place to build the new factory is in Smith County is gaining in popularity.
What makes it difficult is that a long relative clause (that the best place to build the new factory is in Smith County) comes between the subject (the proposal) and the verb (is gaining).
Readers like to get past the subject to the verb quickly. In the sentence above, they can't do that: the relative clause interrupts the movement from the subject to the verb.
Better would be to revise the sentence and eliminate the subject-verb interruption. Here is one solution:
One proposal gaining in popularity is to build the new factory in Smith County.
Now, the verb comes immediately after the subject.
Look at a document you've written recently. Do you see a lot of subject-verb interruptions? How can you revise to eliminate them?