Spray the model with Corax White . Make sure you have a smooth base with this and all of the model is well coated.
Was the whole skin area with Guilliman Flesh in Contrast Medium at a 1:4 ratio. The Contrast Medium should look like it's contaminated rather than a proper mix!
Add a dot more Guilliman Flesh and line in deeper recesses such as fingers, around armour etc.
Use really thin Pallid Wych Flesh to highlight raised areas, such as the shoulders, muscles etc. Use a less-thinned paint to dot knuckles. At some points, the paint should be very thin, as you're glazing rather than edge highlighting, pulling the paint towards the raised areas.
If you're really pushing the contrast, at this point I would add White Scar and do extreme points, such as knuckles.