... I'm not so sure I'd recommend doing any of the above beyond a defrag of a system every now and again and of course, ensuring a system is free of spyware/adaware/viruses. Most of what's listed may free up some memory for better but rather unnoticeable performance while compromising the functions of other programs.
In the end if your computer is not up to snuff to what you want it to do, or is too slow for your patience - then the best alternatives are hardware upgrades... which can be accomplished very easily and on a low budget with more noticeable results that don't have the chance of screwing up your software or OS.
Again... recommend against doing most of what's been put forth (even more so for a novice to computers).