If Ubuntu for some reason crashes and becomes unbootable and unfixable reinstalling will not delete all of your important data and settings. You simply specify the /home partition to be mounted at /home when reinstalling.
Partitioning can end very badly if you dont know what your doing.
To help make this easier, everything we do will be done with a GUI. All of these steps can also be accomplished with the Terminal though.
Procedure to follow
Step 1: Boot into the live CD
Reboot your computer with your Ubuntu (or any live linux cd) in the cd drive and boot into the live system.
Step 2: Partitioning the hard drive
A. Start GParted from System->Administration->GParted
On most systems, /dev/sda is the main partition so we will work with that.
B. You should see all of the partitions on your hard drive. If you only have Ubuntu you will see 2: one is / and the other is swap. Right click on the / partition and select "Resize/Move" Shrink it to however big you wish you /home partition to be.
C. Now right click the free space (it will say unallocated and have a grey square) and select "New" Make it whatever file system you wish, label it something if you want to keep better track of it, and click "Add".
We recomend you double check what you have done up to this point, there is no going back after step D
D. To commit all these changes, click the check mark at the top of the program (it says "Apply all operations" if you hold your mouse over it) This will repartition your hard drive.
Step 3: Reboot and add fstab entry
A. Reboot your computer without the live cd in the drive. Log in as usual. If you have anything important in your /home folder, i recommend copying it to an external of the root drive so you will be able to add it back once you are done setting up the /home partition.
B. Install Storage Device Manager by going here http://packages.ubuntu.com/pysdm
and clicking the version that is for your version of Ubuntu. This will allow you to edit you fstab file and allow the new partition to be mounted as /home.
C. Start Storage Device Manager by going to System->Administration->Storage Device Manager
D. Click the dropdown arrow next to /dev/sda (or whichever hard disk your partitions are located on) and select the newly created partition. If it asks if you would like to configure it click yes.
E. Next to Mountpoint, click the folder icon and goto File System (your root drive), click the home folder and then click open. This will assign the new partition a mount point at /home.
F. Next to options, click the set defaults button. This will mount the partition at boot.
Step 4: Reboot your system
A. Reboot your computer and log into your account. You will have to set ownership of the /home folder with sudo chown YOURUSERNAME /home/YOURUSERNAME before you can copy your files and folders onto it.
Full Credit goes here