I will share my experience with speeding up my website using the WP Fastest Cache and Autoptimize Plugin. Hope it helps many people
Step1: WP Fastest Cache Plugin
1.1 Install the plugin
1.2 WP Fastest Cache Options
Step2: Autoptimize plugin
2.1 Install the plugin
2.2 Autoptimize Settings
Exclude CSS from Autoptimize: wp-content/cache/, admin-bar.min.css, dashicons.min.css