3. See which apps are using the most data
Curious to know which apps are consuming the most data? Go to Settings > Cellularand you can see how much data you've used in the current billing period and below that you'll see a list of your apps.
4. Disable Wi-Fi Assist
Wi-Fi Assist is a great feature where your iPhone hands off a weak Wi-Fi signal to your cellular network to prevent pages from loading slowly (or not at all) as it clings to the last remnants of a Wi-Fi signal. If you sit on the edge of a Wi-Fi network at work, say, then your cellular network may be assisting more than you'd like and running up data charges.
To disable Wi-Fi Assist, go to Settings > Cellular and scroll all the way to the bottom to turn off Wi-Fi Assist.
5. Download music, don't stream
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.
7. Use Safari's Reading List
You can queue up articles while you're using Wi-Fi to read later when you're on a cellular connection or out of range completely. When you add a page to Safari's Reading List, Safari downloads it for offline viewing. To add an article to the Reading List, tap the Share button at the center of the bottom navigation bar and then tap Add to Reading List. If you use iCloud, then it will share your Reading List with your other iOS devices, but you can stop it from sharing via a cellular connection by going to Settings > Safari and scrolling down to the bottom and toggling off Use Cellular Datafor the Reading List feature.
https://www.telegraph.co.uk/technology/2016/04/10/how-to-reduce-your-android-or-iphone-data-usage/
4. Disable background app refresh
This is one for iPhone users only, but turning off background app refresh by entering Settings > General > and either turning off refresh altogether or going through and selecting individual apps will not only help to cut down on your data usage, it has the added bonus of helping to preserve your battery life. Win win!
