Answer

We recommend that you follow the 3-2-1 Rule:

• 3 copies of any important file: 1 working copy and 2 backups
• 2 backups on different types of storage, e.g. cloud and external hard drive
• 1 of those backups should be offsite/geographically far from you, e.g. cloud

You can also schedule your backups according to your needs -- maybe backing up to the cloud every day and the external hard drive every week. It depends on how often you’re making significant changes. 

We also recommended that backups be saved in open or standard file formats, and not be compressed or encrypted (though sensitive data may require encryption). The UK Data Service also has a nice guide to data backups.  Do not use CDs or DVDs as these have been known to fail frequently.