In general I know (or think) you should do things like run registry cleaner, defragment, duplicate finder, spybot, etc... in order to keep you computer running well.
Not really. Registries don't need "cleaning" and cleaners have been known to cause more harm than good (although admittedly, that reputation came about years ago when they were not very refined). If you are not frequently installing and uninstalling major applications (such as office productivity suites and major security programs), your registry should stay "tidy", but even so, having a cluttered registry does not affect performance. But if you really want to use a registry cleaner, I recommend the one that comes with CCleaner because (1) It is very conservative - not aggressive and (2) it prompts to backup the registry before cleaning. During installation, use the custom install option and uncheck the option to install the Yahoo toolbar.
Windows 7 has a built in defragger that works just fine. You don't need a fancy 3rd party defragger. You can spend money on a fancy defragger but you simply waste your money, since fragmentation begins immediately anyway. Duplicates don't hurt anything either - they just take up disk space.
Since migrating to Windows 7, I have moved my systems to Microsoft Security Essentials and Windows Firewall (and IE8) and have no regrets. All have worked flawlessly, have very small resource footprints, and are free. I note that MSE has been certified by all the major labs, and IE8 continues to outscore the other browsers in security.
The main thing is to have a real time anti-malware scanner and firewall, keep your systems updated and patched, and avoid risky behavior, such as illegal filesharing of copyrighted materials (songs, videos and published documents) from P2P sites, illegal porn and gambling sites. Choose an anti-malware program that performs consistently well in tests by the following respected labs: