Start a sentence that the reader can finish. Introduce an idea that encourages the reader to think. You might muddle up two expressions for the reader to untangle, or use parallelism to get readers engaged in unpacking the patterns. Include a puzzle or a riddle. Readers remember more of your message when they get involved in its creation.
Try this
Leave one sentence deliberately incomplete or pose a puzzle your reader can solve.
Ideas
Open a ten-minute sprint with Throw ideas for readers to catch as your prompt.