If you still have the original installation DVD for Windows (assuming you use Windows) and the installation CDs / DVDs for you other software, it is probably easiest to start with a fresh install on the SSD.
You can trim out all the unnecessary stuff from your current HDD (music, pictures, video, etc.), and you may get it down to less than 128gb and then make an image and copy it to the SSD. But my opinion is to start with a fresh OS install on the SSD if you can.
ASUS Maximus V Formula| Core i7-3770K | Corsair H100 CPU Cooler | Corsair Vengeance 16GB | Corsair Force GT 120 GB SSD | Corsair 500R Case | Corsair TX750M PSU | Seagate 1TB HDD | Palilt GTS250 | Win7 Ultimate