I had to opportunity to fish with Butch (Gabowman) who is about as good as they get when it comes to long lining. I will let him elaborate on his methods, but two things were key to his success.
1. He found the fish on his DF before he ever wet a hook.
2. He knew what depth the fish were in and he knew exactly how deep his jigs were running,

When you know the fish are there and you know you are pulling a jig in front of their nose, you usually catch fish, and he does.

SeaRay