To be honest, Gold encrusted cables with some magic powder sprinkled on won't get you a really decent Sky or Freeview picture
The only thing you need to check is make sure your using RGB scart on your Sky STB and not composite. Get a decent quality fully wired scart (nothing with 3 digits!) and make sure the Sky box is set to RGB, click on 'services' on your remote then go to system setup - picture settings, and select RGB video output and not Pal. If your getting a crap picture on the built in freeview tuner then there ain't much apart from tweak the picture which you can do