If you’re willing to put a little effort into search engine optimization, the recognized leader among free plugins is Yoast SEO by Team Yoast. My setup program installed this; even if you do nothing else with it, having it active helps. For instance, it improves the look of your posts when they’re shared on Facebook. And you can do more with it.
When editing a post or page, Yoast adds an analysis panel showing whether the length, complexity, and so on of your content is such as to make search engines happy.
This tells you things like whether your paragraphs are too long, or whether you’ve used passive voice.
There are also fields to set the post description and image for sharing on various social media sites.
You don’t have to pay attention to this tool’s recommendations or satisfy it in every respect, but it’s good to consider its suggestions and decide whether there’s any easy way to make your post more readable and SEO-friendly.