Vary sentence length and pattern, not just in your writing but in your speeches. Create a rhythm that ebbs and flows.
Use short sentences, as I have said before. But don't bore the reader or listener with "See Spot run" sentences. Use sentences of medium length and sentences that stretch the reader's or listener's attention to the breaking point.
Write a one word sentence. Wow. That will help break the monotony. Write ten word sentences that pull the reader gently along. Write fifty word sentences and test the reader's endurance, their capacity to linger with you as you explain some necessary and fundamental thing, as you outline the process you hope to achieve, a process that will eventually serve their needs and result in growth for them and the organization.
Or, bore the reader. Just like this. With short sentences. One after another. Three word sentences. One following another. Or, four word sentences. See how they run? Do you like them? Do they engage you? Not on your life. You annoyed your reader. The reader will stop. Your message will fail.
The reader has other choices, you know. He or she can pick up a magazine, a newspaper, a crossword puzzle, a product label, anything that has words on it, and read it, instead of your memo.
If you lose the reader, you will not communicate. You will just make noise - blah, blah, blah. If you want to keep the reader, if you want to connect, if you want to cause action, vary your sentences. Write a sentence that begins with three subordinate clauses (just like the previous sentence). Or, on the other hand, begin your sentence with a conjunction and a prepositional phrase - just like this sentence. Simple, compound, complex, compound-complex - it's your choice. And remember to keep the subject and verb close together.
Whatever you chose, take the reader on a journey. Stop. On a dime. Take a leisurely walk; over the hills and down through the valleys of your prose, running or walking, skipping or jumping., yelling as loud as you can. Then, stop for a deserved rest. Yes. Here. Wait. Just for a spell.
Now, get your wind. Hurry along with the words gathering behind you before they cascade over your shoulder. (Yes, throw in an image that the reader can see.) Then, slow down again. Stop. Write again. Use three words. Write four word sentences. Keep the reader guessing and interested.
Get along now; pick up some speed; go for the Big One; use a semicolon and join two clauses; and, while you're doing it, throw in another clause, joined to the first sentence. Don't worry. Your readers will follow you, especially when you have used the right tools, such as action verbs, active voice, and characters as subjects in logical prose that sees well chosen words placed within well crafted sentences that create coherent and seamless paragraphs.