Saving data is the most important thing you can do for your pc and most people do not think about it till it too late. You should always have an off site copy of your data. Should theft or fire strike your busines you may be left without  a copy of you most important files.

How often you should backup files depends on when  your data changes and what that information contains. If you use an accounting software daily then your backups should include a daily copy of your accounting program.

What kinds of backups should you do. CD/DVD/HD/Online/Flash Drive are all wonderful storage methods. Some more expensive than others.

What software should I use ? There are too many to begin to  list below are a few I've used or read about.

Basic Backups Scripts
Robocopy
XCOPY

Local backup software
Syncbackupro
Comodo
Handybackup

Online backup software
Mozy
Jungle Disk