Best ways to make a computer more performant

We’ve all come across this at some point, something is inherently wrong with Windows in that after some time it just runs slower. Can any provide any tips/links on how to speed up your computer by cleaning some of the gunk up?

The only two I can think of are:

  1. Spybot S&D to remove spyware.
  2. Removing temporary files from Firefox on close.