This article explains how to save mobile data when connecting your Android tablet to a mobile hotspot or your phone using only Wi-Fi. Instructions apply to all modern versions of Android from 4.1 and up.

If you don't have two Android devices connected (for example a tablet with a Mifi or another mobile hotspot that doesn't support Android, like the iPhone), this hidden setting can be useful:

Open Settings from the all apps screen or by swiping down from the top of the screen and tapping the gear icon.

Go to Network & Internet > Data usage.