Take backups regularly. If you ever need to restore from backup, you'll only be able to recover up to the last time you took backup. Ideally backup should be automatic and ongoing, and not something you need to remember to trigger manually.
You should occasionally test restoring data from your backup solution to make sure that it works as expected. Waiting until you really need to recover data from backup would be a bad time to discover that your backup process was not working the way you thought it was.
Many backup solutions offer a versioning option. With versioning, if there is a problem with the most recently backed up copy of a file, you might still be able to recover a previous version without that problem.
Keep backups separate
Ensure that backup volumes are not continuously mounted on the system they protect. Ransomware will encrypt all data on all mounted volumes, including mapped network drives or file shares.
Caltech has a site license for CrashPlan, a cloud-based backup service. Learn more about the software and service from the IMSS Help Desk.