There is no trick to it, it isn't a matter of washes or drybrushing (though I will occasionally use a wash to colour the highlights, as I did with the Judda). It's just standard layering, you just have to be prepared to leave lots of black (or whatever the base colour is) on show, and only highlight where the light hits and would reflect. You can often hold up a figure and see where the light reflects most, which tells you where to put the highlights. Fight the temptation to highlight just because there is some sculpted detail and if in doubt, leave it black. If you are highlighting an area with light reflected from below (the underside of an arm or leg for instance), stop a couple of highlights from the lightest colour you will use on areas that are reflecting direct light. And be consistent with highlight location, as that is what fools the eye into accepting the shiny look. Best advice I can give though is to have some photos of the real thing handy when painting. Then it is just a matter of practice.