So here is a progression picture and guide to how I paint my Dark Angels marines. Takes me between 4 and 7 hours depending on the day and the model to get a single marine done. I tend to do step one in bulk as a squad and individual models from step 2 onwards

Step 1 - Model on the left

Black undercoat

Caliban green armor base coat

Snakebite leather base for purity seals, skulls, chest plates and pouches

Leadbleacher/Boltgun Metal base for metal parts

Red gore base for wax of purity seals, lenses, gun grips/anything you want red

Nuln Oil is applied over the metal and green areas and very lightly over the lenses

Agrax Earthshade wash is applied over the brown/leather areas and red areas except lenses.

Always paint the guns separately… there is no point trying to be a hero and paint a breastplate from crazy angels where its obscured by a gun.

Step 2 - Model in the middle

50/50 mix of dark angels green and skull white, then thinned with water is painted on all edges of armor. I do a triple line on the shoulder plates, outside and inside edge of the bezel plus a line just inside the inner edge of the bezel, leaving a small black edge in the crevice where the wash will have darkened the armor

This is a time consuming process, rotate the model constantly looking for more edges and lines that can be highlighted, at this point coverage is more important than neatness

Sharper highlights are applied again on the corner or raised edges this time with a lighter 40/60 mix of green to white, and then once again with a 30/70 mix for the final highlights used sparingly

Use water in the mix to make the paint flow, it is better to have the paint too watered down and have to do an additional coat then to apply the paint too thickly and have it dry while still on the brush.

If you accidentally cover a crevice or shaded corner with a highlight, simple repaint the Nuln Oil Directly into the area and redo the highlight if necessary

Step 3 - Model on the right