To use Data Sense in Windows Phone 8.1 to reduce your data consumption, here are two things you need to do:
- In Data Sense, look for “Restrict background data”, and enable it. This means that apps will be unable to use your mobile data in the background
- In data Sense, look for “Browsing data savings”and select one of the options. Selecting “High” gives you the highest data compression
See the two arrows in the screenshot below:
A huge chunk of unaccounted for data consumption comes from apps using your mobile data in the background, so the first tip is essential. The second tip is only important if you use Internet Explorer heavily.