I have a internal 500GB HDD but with only 6GB used. I want to migrate/clone this to a 240GB SSD that will be connected to my laptop through a HD dock.
What is the easiest way?
First you'll need a Live CD (GParted Live should work fine) that you can use to shrink your 500GB disk's partition. You'll need to shrink it down to less than the destination drive size. You should also create a partition of the same size on the SSD.
Then you will burn a Clonezilla Live ISO to a CD, boot from the CD, and clone the partitions from the source drive to the destination drive. You'll follow these steps, except you'll choose "part_to_local_part". You may also need to copy the MBR using options under the "Advanced" menu. You can find more information about that here.