Turn off background app refresh
When this feature is enabled, your apps are constantly refreshing so that they can show you the most recent content when opened. This includes email synching, weather widgets updating, and feeds refreshing. For the iPhone: Turn off the background app refresh by going to Settings > General > Background App Refresh. For Android: Go to Settings > Data Usage > Restrict app background data. This will allow you to turn the feature off for all apps or you can pick and choose which ones you want to turn off.
Disable apps that use a lot of data
There are certain apps that use more data than others, whether you use them frequently or not. For ones that you don’t use often, turn off cellular data. For the iPhone: Go to Settings > Cellular > then under “Use Cellular Data For” switch certain apps to off.
Turn off app updates
If your apps update automatically your phone will start the download whether you are connected to Wi-Fi or not. To turn this off on an iPhone, go to Settings > iTunes & App Stores > turn off Use Cellular Data. For an Android, go to Settings > under General click Auto-update apps > Auto-update apps over Wi-Fi only. Then, your apps will only update when you are connected to Wi-Fi.