Up until recently I've hated most of the Citadel metallic paints. Mithril Silver and Boltgun Metal have been the two exceptions. Why? Because, aside from the two mentioned exceptions, their metallics just don't cover well at all.
I've been getting a lot of e-mails from people recently asking about how I do a particular technique, or how one can improve their painting in some way. The answer is the same as the answer to the question "How do I get to Carnegie Hall?" Practice! Practice!