Ben Yanke coveres the basics

Two big points to be aware of for backups:

1) make sure at least one full copy is offsite, to protect in case of fire or theft

2) make sure one copy, at least relatively recent (perhaps weekly snapshots), is kept on completely cold storage, airgapped from everything and ideally not connected to a powered on system. In the event of a complete systems compromise, there should be absolutely no way to wipe out everything without physical effort as well.