Black can be tough but an easier way I use is to undercoat black, then I highlight zenithally with Vallejo.german grey, then sometimes barley grey. I use an airbrush but if you don't have one just undercoat black, then find a can of mid/dark grey and spray directly down on the model from the top. Then go and put a black ink in some of the deeper recesses that you've just sprayed grey in order to bring the detail out. Very quick and really quite effective.
Not a very good picture, but this is the kind of look you get, still black but highlighted an quite defined.
Automatically Appended Next Post: It's how these guys were sprayed as well before I went back and done the detail, but you can get an idea of the effect.