You’ll have a lower chance to accidentally download a virus and the web is less annoying.
uBlock Origin is the go-to. For Firefox, Firefox on Android and Chrome
Most of you probably already have an adblocker, but an astonishingly large amount of people don’t have one. Try it, you will never go without.
What else do you think is absolutely necessary to browse the web safely?
I know most people browsing this site know this, but you can also enable network-wide DNS-based adblocking with something like Pi Hole. This is especially useful for blocking ads and tracking on appliances and smart TVs.