In situations whereby you have capped subscription. Here's how to conserve your data balance on windows systems.

Here are some tips:

Avoid ‘data rich’ sites that contain streaming videos, large pictures, animation.
Turn of Automatic windows updates.Here's how to turn off automatic updates.
Open Windows Update by clicking the Start button Picture of the Start button, clicking All Programs, and then clicking Windows Update.
In the left pane, click Change settings.
Choose the option "Notify me about updates but don't download"
4. Click on ok or apply and you are done.
Check for viruses as they can eat into your data allowance. If you use avast, avg and the rest disable automatic updates as these updates gulp a large chunk of your data balance.
Don’t use file-sharing/torrent sites. When you use file sharing or torrent applications on your system, you are inadvertently consuming large swats of your data balance as these applications share existing files you have with numerous users thereby costing you examples of this files are bitTorrent, uttorent and the rest.. Goodluck!