Prerequisites: If you have not downloaded the Android sdk, you can download it from here: http://goo.gl/OwiJz. If you are using windows, navigate to Other Platforms> Windows .exe file.
Backing up your device using 3rd party apps can be quite a hassle. Instead, copy the data off yourself using adb.
App data is saved in the /Android/ directory. Save a copy of this directory before reformatting your android system.
To execute an adb command on a linux/mac device, simply navigate to the sdk-tools/platform-tools directory and type
On Windows / PC the location is generally C:/user/Appdata/android/sdk-tools/platform-tools/ command is simply
To copy the Android Directory from your Nexus7 Android Device to a folder simply enter
./adb pull [android-device-source] [mac/linux destination]
On a Nexus 7, this is something like this:
./adb pull /storage/sdcard0/Android/ .
To copy a file or directory from your computer to an Android Device, the command is similar.
./adb push [computer-source] [android destination]
To copy the Android Directory back to your Nexus 7, this will look like this:
./adb push . /storage/sdcard0/Android/