Many mobile phone plans available today to not offer unlimited data. This means is, you should keep track of all mobile data usage on your Android phone.
There are some apps that seem to thrive from having a constant internet connection, even when these apps seem they are not in use. Fortunately for you, Android has offered a way from apps sucking up data in the background.
Built-In Option with Android
Go to Settings > Data Usage for your cellular data usage management. There, you will find an option located on top to entirely disable access. However, use this option only for specific circumstances, such as when you have used more data than allowed by your plan.
To prevent this from happening to begin with, toggle the second option, which is Set cellular data limit.
If your plan has a limit of 6GB per month, you are able to set the limit at 6GB, and when you hit this threshold, the mobile data shuts off automatically. If wanted, have your phone send a warning when getting close to your threshold. Using these settings prevent overage charges.
Looking further down, you will see how much each app uses in data. You want to select heavy users. You should now know which apps should have network access limited. If unable to disable cellular access from their internal settings, toggle Restrict app background data.
Manage Mobile Data Usage With Third-Party App
Grabbing a third-party app lets you go up a level. One open source option available is NetGuard. This app prevents cellular data usage from apps and also stops them from connecting to Wi-Fi. Why would this be helpful? When you block these apps from connecting to the internet, they are unable to track your usage and report it. Benefits include saving battery life, reducing bandwidth, and blocking ads.
Furthermore, you know that your information is not being sent off somewhere across the internet because they do not ask for internet access permission. A VPN is used to block internet traffic, and like other VPN, a key is displayed in your notification bar. Take control over which apps connect to the internet and which do not.
See a list of all your apps in alphabetical order, with a toggle for mobile data and Wi-Fi. You are able to disable access to the ones that you want.
There is a drop-down arrow beside every app allowing you to tap it for specific controls and exceptions.
NetGuard gives you options for block mobile data or Wi-Fi for all apps, under Settings. When you have the screen on, you can set it to automatically allow internet access.
To get setting your fit your needs, you may have to come back and adjust it a few times.