You have not given any details to what risks you are facing.
My way is that I format my PC once a year, first I collect all personal data that I want to keep then do a clean format (including "C" drive) and a clean Windows install. Then transfer all the data back to the PC and Install all necessary programs. This might not seem very practical to some.
I would suggest Downloading Avast the Free version, very light Antivirus.
And Malwarebytes for anti malware, Free version doesnt have live protection so I do scan my PC once a week.
No matter how much you do, there is still a chance of getting risks.
Best way is to watch out what you download and from where. Always double check the URL bar and site reputation. Moreover, keep attention to who uses your PC, I have learned this the hard way, people usually don't pay much attention/care when using someone's else machine.