He certainly looks determined

There are many methods. Two that I find quick/easy/acceptable quality for doing masses of guys:

1- Paint all the flesh a red brown. In Citadel terms it would be Bugman’s Glow, although I have Vallejo Saddle Brown. The exact shade is unimportant. Then layer on the normal flesh color to raised areas. Looking for about 70-80% coverage with the darker red brown in the recesses and crevices. You can continue to highlight up from there but for mass troops this is fine. A dot of black wash in open mouths and put some bone color on the teeth.

2- Paint the standard skin color on and give it an all over flesh wash. I wouldn’t use Agrax or similar for this as it is much too brown. A red-brown wash, such as Citadel’s flesh wash is more appropriate. I have made my own wash out of brown and red inks for a similar purpose. If it is applied too heavily, cleanup with the original skin color paint to bring back the tone may be needed. Highlight additionally to taste.

Man I'm working on Guilliman, and spent 2 hours doing his face. It's not terrible, and not great.

I had to like lay on my arms to keep my hands still, i use a magnifying visor.

And for the eyes, rather than dotting the pupil in, i painted the eye black and dotted a super light gray where i wanted the sclera to be to make the pupil. It took a few tries, and he's just slightly cross-eyed, but I'm happy with it.

You and me both my dude.

Painting faces is BEYOND hard omg

Mouths are doable but eyes are HELL

Helmets are my best friend.

Also I sometimes just do Wraithbone with Guilliman Flesh over it. I tend to just paint to “Battle Ready” so that’s the quickest solution.