Do you want to backup to tape, disc, a network drive or an attached external drive.
If you want to backup to disc or a network share, I would recommend using kdar. You can set up a full backup job, and incremental backups. These jobs can be exported to a bash script which you can run as a cron job.
Another way is to use find in combination with tar or star to backup files modified since the last backup.
Also look in the Linux System Administration Guide. http://tldp.org/LDP/sag/sag.pdf
Chapter 12 covers backups. There is also a chapter on cron.
The manual "Finding Files" provides good instructions on using the find command. I would recommend downloading the source package and producing a Postscrpt or PDF version of the manual. The tar manual would be worthwhile printing out as well. It isn't as good as the Finding Files book, but you will probably need to resort to it as well.