Hi, as a quick guide here is what I would do.
- undercoat in white
- paint orange parts Troll Slayer Orange
- paint black parts thinned Abaddon Black
- wash orange parts with Fuegan Orange
- wash black parts with Nuln Oil (maybe 2 coats)
- wash recesses and panel lines of white parts with very thinned grey. I recommend a ratio of 3:1 Lahmian Medium and Mechanicus Standard Grey.
- highlight Orange by mixing in increasing amounts of White Scar into the Troll Slayer
- highlight the black with the Mechanicus Standard Grey and then again (dotting the corners) either with a lighter shade like Administratum Grey or by mixing in White Scar.
- highlight the white by dotting the corners with White Scar.