Choose your apps carefully. If an app you use has a paid ad-free version use that, if it hasn't then think about whether you would prefer the ads or not having the app.
There are ad-blocking extensions for major browsers, and of course there are browsers such as Brave which build ad-blocking in.
There are non-root ad-blockers, such as Blockada, Block This and DNS66, which use VPNs to filter ads. None is as effective as a good IPtables-based ad-blocker, but those require root. You won't find these in the Play Store, but you can find many in F-Droid or via the developer's own sites (beware of installing apps from uncurated download sites: if anyone can upload apks there, then anyone can upload apks containing malware there).