I would recommend priming with Wraithbone or any other light and slightly warm colour. This will make getting a nice tone to the armour easier.
Basecoat armour with Ushabti Bone .
Either zenethal highlight with thinned Screaming Skull from a downward 45 degree angle or glaze in where the light would hit.
Recess shade with Skeleton Horde thinned with Contrast Medium 1:1. Don't be too neat, the contrast should pull towards the recess and give something like a transition. Now is also a good time to paint the under-suit/tubing by your preferred method.
Recess shade everything again, this time being careful, and using Agrax Earthshade . I used is straight out of the pot, but you could mix in a little contrast if you wanted to make life a little easier.
Add a chunky highlight of Screaming Skull to all edges.
Edge highlight everything again with fine lines of Pallid Wych Flesh .
Selectively edge highlight the most exposed curved edges and corners where highlights meet with a pure white of your choice, like White Scar .
Optional: Battle Damage
Add small patches of Mournfang Brown, using dots with a fine brush. Try to stick to edges and corners where damage would occur, mostly towards the front of the Space Marine.
Underline the damage from the last step with fine lines of Pallid Wych Flesh .
Dark Red Chest Device
Basecoat with Khorne Red .
Pop a little thinned Agrax Earthshade into deep recesses, to darken them.
Edge highlight with thinned Mephiston Red .
Selectively edge highlight curved edges and corners with Squig Orange .
Add dot highlights of Lugganath Orange , where it seems appropriate.
Black Armour Trim
Basecoat with Abaddon Black .
Edge highlight everything with Eshin Grey .
Edge highlight most of the edges again with Dawnstone .
Selectively edge highlight curved edges and corners with Administratum Grey .
Add dot highlights of White Scar to points corners and more exposed edges that were highlighted in the last step.
Red Eye Lenses
Basecoat with Khorne Red
Paint everything but the recesses with Mephiston Red .
Paint the two thirds of the the previous highlight closer to the nose with Evil Sunz Scarlet
Paint the third closest to the nose with Wild Rider Red .
Add a dot highlight of Lugganath Orange , right next to the nose.
Add a dot of White Scar to the corner furthest away from the last highlight.