Desktop:

1.) Use Mullvad Browser with no extensions and don't login to any service.

2.) Use FireFox with Multi Container Extension, ublock and sandbox your sessions with separate containers where a cookie is needed. (Otherwise use Mullvad Browser, see 1.)

3.) Use a VPN with a DNS that blocks all ad and tracking domains

4.) use Torbrowser when possible.

All of the above +:

5.) Use a clean VM with no browsing history, snapshot it. After your're done, restore to clean the snapshot to wipe all browsing history. Or just use Tails OS or Whonix.

On Mobile:

de-google and use grapheneOS.