ok I'll answer
there are quite a few tools you can use to monitor bandwidth. Just google bandwidth monitor.
Things to avoid:
1. Automatic updates (chrome, windows update, etc)
2. Youtube videos. you can watch a few , but videos take the maximum bandwidth .
3. these days webpages are getting fatter, thanks to a lot of heavy javascript and uncompressed images being used by noobs. What you can do, to both make browsing faster and reducing bandwidth usage -
3a. use opera turbo
3b . use noscript to disable javascript on all sites except a selected few.
3c. use load only cached images feature (in opera). for firefox there is a similar extension
link this is a huge bandwidth saver. do use it.
4. don't even think of torrenting.
hth