The industry wide rule of thumb is to run light coverage first. Personally I like to go against the grain when I can. My rule of thumb is to think for yourself. Heavy coverages are prone to hickeys. They also tend to show powder a lot easier if ran on second pass. If you run it through first and you get hickeys it is much easier to run overs to accommodate for spoilage. Heavy coverages can cause sheet distortion but light coverage can as well, and the light coverage is usually more forgiving.
Don't just run heavy coverage on second pass because thats the way it has always been done. Your pressman should know if he can get that coverage through on the down side or not it all depends on the press, the ink, dry times, and durable scratch resistant coating.