This is all just my personal artistic perspective...
First of all, since most manga is B&W, unless you've been specifically instructed to do things in color, I'd concentrate on your skills in B&W.
The biggest thing which jumps out at me about this picture is that she looks like someone chopped off the top of her head and then stuck a wig on her severed skull. Fairly simple to fix, though. See the line which makes the right side of her face (her right, not ours.) It goes up her cheek, out and around her cheekbone, in at the eye, and then up at an angle to her forehead. What you want instead is to have it go out to her eyebrows (and she should have eyebrows,) and then angle back in slightly as it goes up her forehead, because our skulls taper inwards toward the top.
It looks to me like you drew her 'face' and then drew her 'hair' and put them together. Instead, I recommend drawing her entire head and then drawing her face and hair onto it.
Other details: Her neck is a little too far forward--remember, your neck connects in the middle of your skull, not the front or the back.
Her eyes are... oddly shaped. Manga eyes come in many shapes, but triangles isn't generally one of them. Ovals is a good place to start, with large pupils/irises. (She's got really tiny pupils.) In general, in order for the eye to look 'natural', you want the iris/pupil to overlap the top or bottom (or both) of the eye. If it's just floating there in the middle, it'll look weird. <a href="
http://nakedelf.comicgenesis.com/images ... ng">Here's a reference</a>. My comic isn't manga, but the character designs are manga-style derived.
She needs eyebrows. Typically in manga/anime, characters are also given a small fold in their eyelids between the eye and the eyebrow. This is to show that the character is to white. (obviously an Asian character shouldn't have this.) However, I think whether you do that or not should depend on the shape of the eye.
Her ears look droopy. Anatomically, your ears generally line up with the center of your eye and the bottom of your nose. Her ear is going down to the bottom of her mouth.
I would position her nose lower, so that it's not even with her eyes.
This looks basically fine, though I'd recommend changing the angle. Try looking at the situation from directly behind the human's head, say, with the lizard lunging straight at him. It's a nice panel as is to set the scene, but I wouldn't want to just see that--I'd want more closeups and views from different perspectives.
I assume you're trying to play with the screentones/black and whites on this one? As far as that goes it's fine, though it does look like you just want everyone to focus on the boobs and that's a little awkward. Anatomically speaking it's got a few problems.
For starters, breasts just don't look like that if you're wearing clothes over them. You can't get that level of cleavage detail. Also, they're uneven.
Her torso is too short--that or she's wearing her skirt/pants around her ribs. Her ribs are sloping in at an awkward angle for ribs to slope, and she has no hips. (Remember, women with no hips die hideous deaths in childbirth and so get bred out of the species.)
If you extend her torso, then her arms will look proportional--right now, they're too long. Elbows should be about even with the bottom of your ribs, and hands with the middle of the thigh
The left side of her skull (her left) could use some more hair.
Hope that helps, and good luck!
