You walk in with the knowledge of your learning, be confident in that if you are well studied, you must also accept the incompetence of the marker , the ineptitude of the question writer and the absolute irrelevance of many of the question to craftsmen of the trade. accept also that the language is of importance ie; there is a particular language that gets better marks and its not necessarily the language of the trade.
  How do I know this?, I took it upon myself to locate the craftsman exam papers of many candidates, I had them examined by  educational and trade academics. There was a shocking level of inconsistency in the marking, the substandard  language used in the questions often misled candidates.
The craftsman examinations are not reflective of the craftsman plumbing and gasfitting industry.
This is only my take on things, but I know what I see.