Just don't install suspicious files off the internet, duh.
Jokes aside, MalwareBytes is a good option, and make sure to scan any suspicious files through VirusTotal to check if they are safe.
just do a yearly manual scan with MBAM and Avira
Best advice is to run Windows in a Qubes OS virtual machine.
you should only use the built-in windows defender unless you like installing spyware that will make your computer run even slower
although obviously the better option is simply not using windows at all