If you are looking for advice on how to keep your system running optimally, please review the list below.
While there is a lot of advice out on the internet about what to do, please realize much of it will actually cause more harm than it is worth. We could offer our own advice, but there are plenty of people offering tips which we fully endorse.
https://decentsecurity.com offers a great starting place and has some of the best tips and advice all gathered together. Don't use registry cleaners, never disable UAC, and what should you do every quarter to keep your system running smoothly. We highly recommend you review what they have.
https://www.privacytools.io/ offers a lot of resources to keep you secure online.
I'd highly recommend simply upgrading your hard drive or adding more RAM to your computer before you spend any money on tools which claim to speed up your PC. Often times replacing your hard drive or adding ram will cost just slightly more than the applications and will always outperform any cleaning which those applications claim to provide.
There is a lot of advice that will tell you to defragment your computer, clean your registry, disable UAC, disable Windows service, and all kinds of other things to do in order to speed up your PC. I would caution everyone not to use these tools and to avoid turning off any security measures, they can have adverse effects and just are not worth messing with. If you need to defragment your drive please utilize the defragmentation built in to Windows; third party defragments have not been needed since XP.
https://decentsecurity.com will go in to more depth on registry cleaners if you still feel the need to run one
http://www.hofmannc.de/en/windows-7-defragmenter-test/ has great information on defragmentation