Gonna write up a post for you, but I gotta go to class first. Stay tuned :'D

OK, here's what I came up with. I know it looks like a mess, but bear with me.
You need to work on proportions. More than giving you the "learn anatomy" spiel. What I mean by proportions is studying the relationships between certain features on the face and their relative sizes. It's something that I struggle with sometimes too, but it's really important. If you don't get it right, no amount of coloring/detail work is gonna fix it.
Usually what I've seen recommended is that you split the head into an oval, ranging from the top of the skull to the base of the chin. In this model, the eyes are pretty much dead center. You can then split the bottom half into two, the middle line showing where the nose goes. Then repeat once more to place the mouth. Ears are typically from the top of the eyebrows (slightly above the eyes) to the bottom of the nose or so. This gets the face about right. You'll want to add a little bulk to the sides to complete the skull. Play around with these proportions a bit to get the gist, then feel free to experiment!
A few extra things I thought I'd mention: when drawing men, you'll want to use more bold lines and strokes, compared with more subtle or understated strokes when it comes to women (this is generalized, of course). Some other differences include that men typically have a stronger jaw line, a thicker neck, a heavier brow ridge, a longer nose, and a thinner mouth. Men typically also have a lot more muscle definition, even if you're going for the shrimpy guy look. Also, if you wanna go for the anime cliche, you can also include smaller or narrower eyes.
But perhaps more importantly than even all of this is to start understanding the basic form of what you're drawing. You're trying to show a 3D shape in 2D. A few points that'll help you achieve this are learning about perspective and form. When you say you want to include more contrast in your work, then this is exactly what you'll want to pay attention to. Start off drawing things like spheres, pyramids, boxes, etc in perspective. Work your way up to more complicated shapes. Vary the lighting. Drawing from life will also help.
http://www.sheamusburns.com/?p=274 << example of how to draw a box & light it
(There was another really good tutorial that I found awhile back, but I can't seem to locate right now. It had one part that showed you how to draw a ladder and include a light source, too. Very informative.)
http://www.anticz.com/heads.htmhttp://www.anticz.com/drawing1.htm
<< Here's two tutorials I found that look promising.
And lastly, what I'd suggest is to sketch out the basic skull shape before going in to add all of the details. This can help you avoid issues where the head is cut off due to the hair (aka flat-head syndrome).
Ah, and on an unrelated note (last thing, I promise!), you'll want to look at some references when drawing anything. By reference, I don't mean copying exactly what you see necessarily. More, you'll want to get the "gist" or "concept" of something. If you were drawing a dragon, for example, you might look up lizards, bat wings, dinosaurs, birds, etc. Since you want a mer-man type of character, why not look up fish? Or other types of creatures? The zora from Zelda keep popping into my head.
Any questions, feel free to ask me. I'm a bit tired as I'm writing all this and I fear I might be rambling. xDD Anyhow, good luck.