Additionally, use Wi-fi as web access as often as possible. Wi-fi access doesn't count against data limit.
There are 5 family members on our (wait for it) Family Plan here in the U.S. As said previously, down loading videos (and music) eats up the data allowance muy pronto. We have Wi-fi connectivity in our home which we needed for effective access for Mrs. C's Kindle, but that access alone has saved plenty of overshoots on our data plan which is only 3GB worth. Couldn't so it without the Wi-Fi. So much so that I carry a device from the phone service provider (Verizon) called MyFi that creates Wi-Fi access when I'm on the road, so to speak… just plugs into the computer and voila!