For the first image, the character is not in perspective with the background. From what it looks like i think you're going for a 3 point perspective shot? As everything is kinda angle to point up to the top, if not lemme know and ill throw a red line at you C;

As for the rest, since jjjorgie had already cover most of the stuff, just wanna point out a few things, i notice with the shading style that you are trying to go for of then the nose end up looking as if they are not align very well with the overall face. They tent to lean to one side. I know you cant flip traditional drawing, but what i like to do when sketching on paper is to hold the paper up against the light, and look at it from the back, that way the image is flip and you can try to spot out the mistakes.

Also, this could be personally preference, but i would try to simplify the shading around the face, and keep the face area with as little contrast as possible. That way it can pop out a bit and catch the eye easier. But thats just me ;D