This topic could cover pages of suggestions and issues. We will cover just a few simple steps to keep your workstations running well.
Step one is to have a good anti-virus program running and performing active protection. Most workstations are shipped with a trial version of an anti-virus already in place.
Step two is to run a scan of the workstation on a routine basis. This should be done utilizing a different anti-virus software. There are many secondary scanning tools available. Hitmanpro (http://www.surfright.nl/en/hitmanpro/ ) is a good example of a secondary scanning tool that can be used for free. The frequency with which you run a secondary scan should be determined by how you use your workstation.
Step three is to keep your workstation current with updates from the various software packages that you use. Hackers are constantly finding and exploiting "holes" in software. Once they gain access, they usually disable any anti-virus software.
Finally, the best protection is common sense. Do not open email attachments unless you are expecting a specific email with an attachment. Do not follow links within an email as they can be easily disguised. Be aware that simply visiting a bad website can infect your workstation. Also, be aware of the performance of your workstation. If you have random pop-ups, the system is slow or if you are sent to a webpage that you did not expect, run a scan. Whenever something is found or suspected, change all passwords to various online accounts.