If you want to implement a serious backup strategy, you should have about 250GB of external space on an external disk.
The easiest is with images. That is a "catch all" if you have only one partition for the system and data. It is, however, preferable to have a seperate Data Partition
. Then you can Image System and User Data at different times depending on the change activity. A sperate data Partition is also useful if your System goes on the blink - for whatever reason. The manipulation of the System Partition will then not effect your user data.
To get you started, have a look at this: Imaging with free Macrium
And if you like to know more about good backup strategies, read this: Imaging strategies