I bought a lenovo k3 note recently and using Google now launcher.Today I was shocked to see that nearly 1gb of my data was used by Android OS in background.Is it common to every one. 
Unusually high data usage by Android OS? - 1
santosh kumar
On your device, go to Google Play, find the settings WITHIN the app, and make sure it is set to Only Update Apps Over Wi-Fi
Now it should never update apps over cell data unless you manually tell it to.
I also keep both cell data and Wi-Fi off except when I need them, and I only turn on one or the other. I turn off GPS and set Location setting to the lowest offered (may be Off or Battery Saving).
I turn off Google Now - Google Now listens to what you say, listening for "OK Google" and may be using data to analyze online what you are saying.
My personal choice is I turn off every Google feature that would use bandwidth - I turn off Sync, Backup, Gmail Sync, etc. I don't need to get my mail on my phone (of course you need to not mind losing everything if something goes wrong with your phone). If I do need to send or read mail then I need to use the browser and go to gmail.com (Gmail app won't work with Gmail sync turned off).
I also don't install piggy social networking apps. I don't want somebody else's stupid Facebook etc posts eating up MY cell data. I do use a Twitter app but it seems to not download messages unless I open it.
I get OVER A WEEK of standby on one battery charge. I'm a light phone user - couple of calls and a few texts per week, maybe play a game at lunch, view/take/show a few photos. When I charge the phone every Monday I often have over 50% battery remaining. I occasionally use cell data at a restaurant (if they don't have Wi-Fi). I have no need for cell data to be on all the time.
cathugger