I spend a complex of works:
1. I configure the correct caching.
2. I check if compression is enabled on the server.
3. Compressing (optimization) all images on the site, regardless of their number, for free (! )
4. I adjust the lazy loading of images, video, iframe.
5. Minification of style files and scripts.
6. Combining style files and scripts.
7. I configure the postponed loading of styles and scripts.
8. If necessary, I configure and connect the critical css.
9. Inspecting plugins, leaving only used working plugins, the rest I deactivate.
10. Disabling all unused scripts and styles on the pages, leaving only what is used on the page (! )
11. Cleaning the database.
These are only the most basic and important points, in fact, they are 2 times more.
The necessary plugins will be connected to work (usually the most optimal bundles are checked and selected taking into account the features of a particular site).
Depending on the package you choose, I usually manage to achieve the following results on Google PageSpeed Insights:
on the desktop - 75-96,
on the mobile - 40-75.
Also much will depend on the abundance of ad units and affiliate widgets on your site.