Should link you to album with some images, if not I guess I will post shit one by one.

Most of these are school projects.

Im shit at 2D so no judging.

Gimp was used

Edit: forgot link

http://imgur.com/a/QdwDk

Edit Edit: the cards were made by me and a friend.

First of all the only thing we can do is give judging/ CnC
The head is really deformed it looks like an alien except on the
knight. The knights armor makes his arms look like the shoulders
aren't there the landscapes have an interesting style i like it but the
first landscape still needs some line work it looks like.
Just try to keep your lines go through with them instead of leaving
random ass black spaces also here is some head development sketching
that you can add your own touches to etc...

the poses are good and the idea was cool.

some critiques from my personal view of it,
You should draw with construction forms inside of each thing you draw.
here is my way of construction,
it starts with the pose, I use line of action the most for this.
Then you should think of simple 3d forms you can draw and construct the body, this is the concept for everything you draw.
I put flow, but consider it just for hair, with hair you need to make it flowy and follow the motion of the hair, consider gravity, wind and movement.

Now lets see what I came up with:

You should note that the way I drew this is from andrew Loomis way,
I drew an sphere with plane, adding forms of anatomy later.
the body follows the first pose, You should state what is in front of what,
as the character is turned to his foward a bit, I drew the shoulders smaller and the back shoulder behind the chest.
the rest is okay, My hands werent that perfect, so, dont mind.

About the shading,
you should start with a midtone, then go to shadow and light, try to block where the main tones are before the blend in, it helps you to not lose control of the painting and go straightfoward.

I supposed it as front light, so I put the lights and shadows to follow this lighting.
I didnt blend in and got a good look yet doing it wisely.
Last part of my CnC is about the lines, as you can see My real dark color Lines are just for edges of colors, they arent thick or anything, You have to give lines to a realistic drawing where it fits, go and look at reference to see what edge of color has anything like a like, dont forget to use the real colors for the lines instead of black.

concluding, I like your effort on this, do not give up, going from heads to real drawings is a hard improvement, keep drawing and you will improve more.
I hope it helps.