The face is a tricky to get right, with so much going on. It really helps to know your style to know what you want to do with the face, and that comes with practice. One rule you'll probably want to keep in mind is to put the eyes near the middle horizontal line in the circle that represents the head. There needs to be room for the eyebrows, forehead, and hairline, otherwise the character won't look right. I've found that simpler noses tend to look better, and lips can be a simple short curve or the more pronounced Adam Warren style. I like the big pouty lip look, but it can be difficult to pull off. Hair is also a problem, and there are many approaches to it. I usually try to keep things as simple as possible, using only a few outlines. Here is the face in detail as well as the full picture so far:

By this point, I'm ready to more carefully chose the final lines from my sketching by darkening in all of the outlines and add any details to the character. Here I added some clothing and tattoos: