4. Refresh (F5) the desktop after closing any application. This will remove any unused files from the RAM.
5. Empty the recycle bin regularly. The files are not really deleted from your hard drive until you empty the recycle bin.
6. Defragment atleast your boot drive (may be C:) once every two months. This will free up a lot of space on your hard drive and rearrange the files so that your applications run faster.
7. Always make one more partition (Drive) other than your boot partition and Install all heavy Softwares (like Maya, Photoshop, 3DS Max etc) to the second partition and Keep the C Drive as empty as possible. This will reduce the O/s loading time.
8. Disable the option of starting the application automatically when the PC boots. This can be done by using the MSCONFIG Utility. Open RUN Command (windows key+R) and typemsconfig and hit enter key you can see a tab named startup, uncheck everything you don't need.
9. Protect your PC from dust. Dust causes the CPU cooling fan to jam and slow down it and thereby gradually heating your CPU and this will affect the processing speed.