If your apps update automatically. Change your setting so that apps update only when you are on WiFi.
Settings >iTunes & App Stores and turn off Use Cellular Data.
2. Disable Background App Refresh
iOS apps can be updated in the background. Apps get updated with the new content in the background as they can show the latest news when you open the app next time. This setting can be turned off completely. We can also select the apps that we need to update in the background
Settings > General > Background App Refresh
3. Disable Wi-Fi Assist
Wi-Fi Assist is an awesome component where your iPhone hands off a powerless Wi-Fi sign to your phone system to keep pages from loading gradually or not in the slightest degree as it sticks to the last remainders of a Wi-Fi signal. On the off chance that you sit on the edge of a Wi-Fi system at work, say, then your cell system might be helping more than you’d like and running up information charges.
Settings > Cellular and scroll all the way to the bottom to turn off Wi-Fi Assist.
4. Disable iCloud Drive on Cellular
If you use iCloud Drive to shuttle documents in and out of the cloud, those data transfers can add to your bill if they are done over a cellular connection. You can restrict iCloud Drive to Wi-Fi.
Settings > iCloud > iCloud Drive and scrolling to the bottom and turning off Use Cellular Data.
5. Download Music, don’t Stream
Streaming music or podcasts for long stretches when you are away from Wi-Fi can quickly add to your data usage. Most music and podcast apps (like Spotify and Apple Music) let you restrict streaming to Wi-Fi only, which will then force you into the habit of downloading playlists or podcasts before playing them instead of the easy route of simply streaming them. Let’s look at Apple Music and Apple’s Podcasts apps as examples.
For Apple Music, go to Settings > Music. In the Streaming & Downloads section, you’ll see two settings if the first is enabled. The first, Use Cellular Data, lets you disable streaming via a cellular connection entirely. If that’s too drastic a measure for you, then you can leave that setting enabled and turn off High Quality on Cellular to stream songs at a lower bitrate when you aren’t on Wi-Fi.
For the Podcasts app, go to Settings > Podcasts and turn off Cellular Data. You can also enable ” Only Download on Wi-Fi” to prevent podcast downloads from adding to your data usage.