From Van's, here's their guide to tightening nuts (from a page in their excellent chapter 5):
For tightening flared fittings such as brake and fuel lines.
Similar info, but also useful
Good video on tightening flare fittings
For tightening NPT fittings (the left side of the picture below. The right side is a flared fitting which is tightened as described just above). It's suggested to use Loctite 567 for the NPT threads.
