Use short sentences interspersed with long sentences. Keep it interesting, but still easy to read. Challenge people with your message, not with jumbled language misuse.
Use long sentences wherever necessary, of course. Use short sentences relatively often, but not to the point that your writing sounds choppy.
Simplify. Break down your message into simple truths, encapsulated by simple sentences. Even if the sentence is long, it should still be easy to read.
Any sentence that looks like a paragraph by itself is almost certainly too long. On the other hand, a paragraph full of short sentences will sound monotonous.
When you utilize a variety of sentence lengths and structures, you will inject an engaging sense of rhythm into your writing.
So, mix it up!
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