windows 7 - What is the best way to 'clean' my computer?

I am currently running Windows 7 x64. I frequently install, uninstall, modify, break, or otherwise alter various programs on my computer (experimentation is fun!). Anyways, over the past six months (how long this version has been installed) I have noticed an obvious decline in my computer's performance. I have been expecting this, so over the past months I have regularly 'cleaned' my computer - removing programs, defragging, CCleaner, and virus scans. I know that it isn't possible to reverse every action that installing or deleting a program causes, but I have a feeling that I can reverse more of these effects and speed up my computer. Lastly, on top of cleaning, I have also disabled all of my startup processes besides the vital ones that I need to run my computer.

So, I guess in conclusion, are there any more steps that I could take my clean my computer more effectively in the computer? I know there are different versions of programs such as CCleaner, and there are uninstallers besides the Windows one, but I don't know if those actually make much of a difference. Would anyone have any recommendations on how to better clean my computer in the future from random junk, settings, etc. That I no longer use or never do?

Answer

To add to the existing answers. Uninstall with Revo Uninstaller. This will find all files and registry entries associated with the uninstalled program. You choose which of these to actually delete. It will also automatically create a restore point, should you accidentally delete important files.

I also sometimes use WinDirStat. This will create an overview of all the files on your hard drive. It also gives a graphical representation of the used space. This is handy to find large files that are left behind (some iso for a VM, for example).

Do some scans for other malware (you only mention viruses). I use MalwareBytes and Spybot S&D.

If your boot is becoming slower, use Soluto. If you're an advanced user, you might be better off with Autoruns.

Also consider that your hardware itself might have become slower over time. Especially if you're using an SSD, wear can become noticeable in a relatively short time.

You might also want to try and find whether there's any software slowing your PC down. You're best off with Process Explorer for this. It shows all information about all the running processes. (seriously, it shows everything you would ever want to know about a process, and more)