How to optimize WordPress theme?

Hello good people,

In recent days speed optimization is the hot cake in web industry. Almost all search engine express their thinking about website loading speed.

Website developers are noticing these days about speed optimization jobs from their company / clients.

Specially, WordPress developers are facing this slow speed issues. Because, page builders like Wpbackery, Elementor generates tons of codes (DOM, Js, Css).

Would you please share your thoughts about the speed optimization factors and how you improve it?