The fastest and most effective way is to spend some time in a country where English is the main language. If you can’t do that, the next best way is to make friends with native English speakers in your own country. The third best way is using apps such as HelloTalk or Tandem, which enable you to talk to people whose mother tongue is English. If they are learning your mother tongue, it’s even better because you have a fair exchange of effort
Just checked: my YT account is old enough to be starting its first year of uni. Guess I don’t have to worry about accessing adult content, but ye gods I’m auld…