Here is how I painted the armour, trim and eye lenses of my Imperial Fist Space Marines. I have a separate guide showing images for the yellow armour only.

Yellow Power Armour

1. Basecoat armour with Averland Sunset .
2. Either zenithal highlight with thinned Yriel Yellow from a downward 45 degree angle or glaze in where the light would hit.
3. Recess shade with Iyanden Yellow 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.
4. Recess shade everything again, this time being careful, and using thinned Mournfang Brown .
5. Selectively recess shade with thinned Rhinox Hide , aiming for the very deepest parts.
6. Add a chunky highlight of Yriel Yellow to all edges. Alternatively, you can mix a vibrant yellow like Flash Gitz Yellow with the Averland Sunset from earlier.
7. Edge highlight everything again with Yriel Yellow and Screaming Skull mixed 1:1.
8. Selectively edge highlight the most exposed curved edges and corners where highlights meet with Screaming Skull and a pure white mixed 1:1.
9. Add dot highlights of a pure white like Dead White to the centre of the previous highlights and points/corners.

Battle Damage (Optional)

1. 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.
2. Underline the damage from the last step with a 1:1 mix of Screaming Skull and Dead White .

Red Trim

1. Basecoat everything with Khorne Red .
2. Glase large flat areas and places where light would hit with a 1:1 mix of Khorne Red and Mephiston Red .
3. Add a chunky edge highlight to these areas with Mephiston Red .
4. Highlight everything again, this time with Evil Sunz Scarlet .
5. Selectively edge highlight prominent edges and corners with Wild Rider Red .
6. Ad spot highlights of Wild Rider Red and Lugganath Orange , mixed 1:1. Add this to the centre of the previous highlights and points/corners.

Blue Eye Lenses

1. Basecoat lenses with Kantor Blue .
2. Mix Kantor Blue and Temple Guard Blue 1:1 and glaze over the centre of the lens, dragging the brush towards the nose.
3. Add a small highlight of Temple Guard Blue , covering two thirds of the centre closest to the nose.
4. Add an even smaller highlight of Baharroth Blue , covering the inner third closest to the nose.
5. Add a dot highlight of Blue Horror , right next to the nose.
6. Add another dot highlight, using a pure white (like Dead White ). This should be placed in the opposite corner, closest to the ear.

Green Eye Lenses (for Sergeants)

1. Basecoat lenses with Caliban Green .
2. Mix Caliban Green and Warpstone Glow 1:1 and glaze over the centre of the lens, dragging the brush towards the nose.
3. Add a small highlight of Warpstone Glow , covering two thirds of the centre closest to the nose.
4. Add an even smaller highlight of Moot Green , covering the inner third closest to the nose.
5. Add a dot highlight of Gauss Blaster Green , right next to the nose.
6. Add another dot highlight, using a pure white (like Dead White ). This should be placed in the opposite corner, closest to the ear.