Windows 8 is an already performant operating system but with some simple tricks you can optimize it and make it more faster without any software need!
you can optimize the OS booting by disabling some services. Press CTRL+R then type services.msc.
You can understand services by description and choose to start them manually or automatically or set disabled. You can also refer to How-To-Geek or Computer Unleashed post and see a list of services that can be safely disabled
you can also disable some not needed programs from startup. Just open Task Manager and look at the startup tab
adjust visual effects
especially in old pc, you can set the adjust for best performances or for best appareance or set manually. In control panel -> System -> Advanced system settings -> Advanced tab and then select Settings under Performance section
disable live tiles
right click a tale in Metro screen, click the turn Live Tile Off button to disable