Windows can get itself into a bit of a mess sometimes and cleanup's can help. But certainly don't recommend bundled clean up tools or any that want you to pay for them.
Defragging - Fine if you have a HDD (hard drive) but unless you're constantly moving around masses of data once a year is fine. DON'T defrag Solid State (SSD's)!!!
You have Avast, but always a good idea to run a separate Anti-Malware program, Malwarebytes is good. Stick with the freebie, don't bother with the trial upgrade.
CCleaner - IMO a great cleanup tool. It will empty caches, and temp folders bringing back space and the registry cleaner is good too (but do backup the registry when prompted just in case). Also, providing your computer's running fine, I'd go into the tools section and cleanup your system restore points too.
Lastly I also like the built in Windows Cleanup tool. Right click a drive and choose properties and you will see the windows cleanup option. Is you do the cleanup system files option too it will clear down old windows update files etc.
Other than that, you can check your drivers are up to date and Windows updates are all installed. If you're using Internet Explorer, stop, download Google Chrome or Mozilla Firefox browsers instead as they are much faster.
If it's still slow you might want to consider backing up your files etc and doing a full rebuild of Windows.
Also check you have enough ram in your system, these days I'd say 4GB minimum if it's a 64bit OS? If you have the funds and your pc has a reasonably recent spec (say up to 5 years old) changing from a HDD to SSD will give the best and a very noticeable performance boost. You can also do that fresh Windows rebuild at the same time.