Here are some optional plugin which you can use for your website optimization.

Compress JPEG & PNG images : https://wordpress.org/plugins/tiny-compress-images/
W3 Total Cache: https://wordpress.org/plugins/w3-total-cache/
Leverage Browser Caching :https://wordpress.org/plugins/leverage-browser-caching/
Autoptimize: https://wordpress.org/plugins/autoptimize/
WP Admin No Show: https://wordpress.org/plugins/wp-admin-no-show/