Updating a 2008 iMac from Leopard to Mavericks

As the title says, I am about to update an old iMac (2008 model) running OSX 10.5.8 to 10.9. There has never been any kind of maintenance or disk clean up on the machine. Is there anything important I should do before updating it to Snow Leopard and then Mavericks? Any and all tips, big and small are appreciated.