A problem which you may occasionally encounter is the unexpected loss of some of your work and settings for one reason or another. The causes of such data loss are many and varied; it could be anything from a power cut to accidentally deleting a file. It is highly recommended that you make regular back-up copies of your important files so that, if you do encounter a problem, you will not have lost those files.
It is wise to store back-up copies of files separately from your computer; that is, you should make use of some form of file storage which is not permanently attached to your computer. Options include:
Writable CDs and DVDs
External hard disks and flash memory devices
Another computer on the network
A simple way of backing-up your files is to manually copy them to a safe location (see above) by using the File Browser.
Alternatively, you can use a dedicated back-up application, such as HUBackup:
1.Install the hubackup package from the “Universe” repository (see Add Applications).
2.To make a backup, press System → Administration → Home User Backup.
3.Select the files which you would like to make a backup copy of and choose the location which you would like to save the backup to. If you have a CD or DVD writer, it should be present in this list.
4.Press Backup and follow the instructions given on-screen.
To restore a backup made with HUBackup, press System → Administration → Home User Restore and follow the instrctions on-screen.
Some general advice on how to keep good back-ups is given below:
Back-up on a regular basis
Always test your back-ups after you make them, to ensure that they have been made correctly
Label your back-ups clearly, and keep them in a safe place
source : http://help.ubuntu.com
good luck !!!