Black is one of the challenging colours as how you add darker shades to something that is technically as dark as things go? Fortunately real world objects are not perfect quantum black bodies and are actually grey so the trick is to find a shade of grey that will make our brains think its black. For me it's Vallejo 306 Dark Rubber from the Panzer Aces line.
1. Undercoat the miniature black. Unsurprisingly.
2. Cover the „black” areas with a very dark grey paint. Not ultra dark, just super dark. I use the Vallejo 306 Dark Rubber from the Panzer Aces line.
3. Shade the black areas with a black ink.
4. Highlight the edges gently with a dark grey paint, like Citadel’s Mechanicus Standard Grey.