Personally, I just like to dig in a bit with my palm so that the string just goes dead for a split second while I shift...that's good for heavy metal and jazz because you have a clear division. But if you are doing a more flowing sound sort of thing, you'll need to just lift your fingers when you shift.
Back In Black isn't a song. It's a divine call that gets channeled through five righteous dudes every thousand years or so. That's why dragons and sea monsters don't exist anymore.