I know this is all very 'after the horse has bolted', but when you install, create a partition for / a partition for /home and a swap partition.
There will be many people who will say create a partition for /boot and one for /var etc. But, for an example, / needs no more than 10GB, swap roughly double the size of your RAM, and the rest for /home.
That way next time you mess up and want to reinstall
you only need to format where / is and not the partition you'll mount as /home.
/home is /dev/sda5 on my system, and in the last month I've installed Ubuntu, Debian and Fedora, every time mounting /dev/sda5 as /home, and obviously enough, never lost any of my stuff.