Some very influential things can be done in this regard on most stock vendor Android OSes already as a user:
- Not using a Google account from the start or later (the Google account step can be skipped in the initial Android user setup, or an existing account can be removed later in the account settings).
- Uninstalling preinstalled Apps you don’t like via the standard Android way (which is via ADB … Uninstall default apps - #29 by AnotherElk).
- Really checking the Settings … all of them. There’s a lot of Google stuff that can be disabled or minimised, if you just realise it’s there and there’s a setting for it.
That already takes care of a lot.
If you really want to get into it further, you can of course try to reproduce certain technical steps that get incorporated into /e/OS, at least as far as your stock vendor Android OS allows, it’s documented what /e/OS is and does … https://doc.e.foundation/what-s-e (which also includes a link to this white paper).