Make full use of variety. Write to express, not impress. Question any word over three syllables. Little people use big words, big people use little words. Don't hedge your prose with little timidities.
Good writing is lean and confident.
Don't diminish your authority, make your reader believe in what you write. Don't be kind of bold. He showed how to use the changes that were made on the engine. In so doing you divert the reader's attention to yourself. State what you think, give your opinion, tell what you believe.