Canonical lists just over 30 Linux viruses and worms in its published malware list. In contrast, there are about 140,000 viruses for Windows, so...
If you dual-boot with Windows, run Windows in a VM, use WINE or simply share files with Windows-using friends, scan the files for viruses.
Enable the MATE software firewall, if it isn't already. (See below.)
Keep your system updated. Updates are automatic on most Linux distributions. Let them run as soon as they are available.
Use strong passwords. On everything. And use a secure password manager to store them.
Make backups regularly.
Install software only from trusted sources, like MATE's Software Boutique or software repositories.
Use security-related plugins for your Internet browser that protect your data, credentials, and privacy.
Use your common sense. The biggest security threat is generally found between keyboard and chair.