NetGuard is amazing, really can't recommend it enough.

You can use it to specify which apps are allowed to use WiFi/data, and whether they're allowed to use all the time or only if screen is active. It also allows you to set a hosts file URL and update it with a single click. It has improved my battery life, I rarely see ads (both when using the browser and when using apps), and it force me to use old.reddit.com since reddit.com is blocked by my host file.