Simple fix for Windows 8.x or Windows 10. In your Network settings you can go into your Wireless SSID and set it to a Metered Connection. This disables a lot of background activity that uses data up.
http://windows.microsoft.com/en-US/windows-8/metered-internet-connections-frequently-asked-questions
Don't confuse data usage with the user privacy issues that the main stream media is all over like flies on s#$@.
This is a good novice friendly primer of privacy settings and Windows 10 "phoning home", but mildly on the paranoid side.
http://www.pcmag.com/article2/0,2817,2489212,00.asp