• DO - BACKUP as often as needed to protect data you are not willing to lose
• DO - use ESET Antivirus (we sell it), you don't get much for free
• DO - install CRITICAL Microsoft security patches and updates
• DO - use Malwarebytes free edition as a second opinion scanner
• DO - check your defragmenter schedule and that it runs
• DO - empty emails deleted items and the computers recycle bin every week
• DO - compact mail folders in MS Outlook every 90 days
• DO - enable Windows firewall - generally this is all you need and very dependable
• DO - minimize the number of icons/programs in the system tray
• DO - mind static electricity when handing over flash drives
• DO - set a secure Wireless Network Key for wireless routers
• DO - uninstall all versions of Java unless you need it
   
• DON'T - let your "C" drive get over 75% full
• DON'T - install demo software - many are unstable
• DON'T - install free stuff** - you may get more than you think
• DON'T - install software that may not be for your version of Windows
• DON'T - adjust BIOS settings unless certain of the need
• DON'T - leave Bloat-Ware checked (UNCHECK IT) on Adobe, Java and other updates
• DON'T - Install Java unless you need it, many infections use Java

** You get what you pay for so if it is free someone usually ends up paying something in advertising, lost time and/or productivity and someone else is gaining. 
There are some exceptions but they are less common.

Please call if you need help