This is how I do it. I neglected my hands in this photo (put camo on before chow, medic makes us wash our hands before we eat...), and I didn't go down my neck far enough (durn sagging t-shirt). But, it was enough that the Sergeant Major didn't complain, though he did finally get after us for not wearing our chinstraps properly.
I was never taught any special way of applying camo paint, though the ROTC cadets do go on about applying certain colors to certain parts of your face. Whatever.
It does seem to make my face blend in with the rest of me. So, my face is at least as camouflaged as the rest of my carcass.
Note: Camo paint and glasses don't always go well together.
If applied properly, camo paint will be an absolute ***** to get off, as you'll have covered your ears, neck, face, etc. It gets up in my (fairly thick) eyebrows, for one, and takes a healthy scrubbing to get off.
DO NOT use the Army-issue camo sticks. They're the hardest to get on, the hardest to spread, and they make most people break out. I prefer the cream that comes in the tubes, but most guys have the little compacts.
It tends to come off with sweat (especially if you wipe the sweat from your face).