For a classic ‘Eavy Metal (blue/black) style do not start with a pure black basecoat. Use a dark to very dark blue (i.e. 50/50 regal blue and chaos black). Then shade down the area with a chaos black glaze into the recesses to create depth. You can then re-apply a thin coat of the base coat to the more prominent areas.
For the next stage add a little space wolves grey or similar off-white colour to the earlier mix and paint on the most raised or reflective areas. For the final stages paint a very fine highlight of pure space wolves grey (very sparingly) on sharpest edges and most reflective areas.
Use the highlights sparingly to avoid the loss of the black effect. The new citadel paints seem to incorporate these stages and the blue/black progression they have created appears to be based on this concept although you would need to go up to a lighter highlight stage for the final highlights.