How fast the webpages are loading is also an important item to solve, and that involve optimizing the images (the format and size are important) and making them load only when the visitor is on each of them (lazy loading), defering or delaying the javascript execution, minifying the css and javascript files and even combining them to load one file not many.
Yoast SEO is the most known search engine optimization (SEO) plug-in for WordPress. It has over 5 million active installations and has been downloaded more than 350 million times with 25.832 five star reviews on Wordpress.org.
If you want a different seo plugin you can use WP-Optimize - Clean, Compress, Cache - it makes your site fast and efficient, it cleans the database, compresses images and caches pages. It's working just fine, but you should be checking the deferring and delaying javascript - it may interact with your Wordpress theme.
WP Super Cache is another very fast caching plugin for WordPress you can be using.
Cache Cleaner - Scheduled cleans up your cache from time to time, depending of the period you are setting.
Lazy Load - Optimize Images - this tiny Lazy Load script for WordPress optimize the images loading and YouTube video without jQuery or others libraries (if you don't want the lazy loading from WP-Optimize).
XML Sitemap Generator for Google creates HTML, RSS and Google XML Sitemap generator compatible with Google, Bing, Baidu, Yandex and a few other search engines. It can only help finding pages on your website.
WP Crontrol enables you to view and control what's happening in the Wordpress cron system. Removing the unnecessary cron tasks makes your website faster.
Performance plugin is a collection of standalone performance modules that also improve the speed of your Wordpress.