First, I applaud you in putting yourself out there to try to improve in what you do wrong....in front of strangers who could say anything, that takes strength just to let you know.
mrgreen
I think the problem is that your your working with a new medium(the computer) and you're having a hard time with anatomy, so already at a huge disadvantage, so don't be hard on yourself!
Let's talk about anatomy first.
For instance, I know that her eye isn't a long slit because how the eye ball itself sits in the socket of the skull and how the human skull is constructed, I know that her right arm's bone is too elongated, she wouldn't be able to use her hand based on her skeletal size and structure.
Without the why of anatomy(how muscles,bones connect and their use) it will look off. You don't have do know every bone and muscle, but the major parts helps to know what looks off.
Why aren't doctors artists, well to draw realistically,the easiest way(In my opinion) is to break down the human form into geometric shapes/forms, reading them as such which takes a lot of practice oberservation. You can use lines as well, especially when doing with gesture, capturing the emotion of a subject but it's better to understand anatomy before manipulation, I found out that the hard way. Both are equally valid and important though, don't get me wrong.
Let's look quickly at the most common geometric shapes for reference:
Now by adding contour lines or lines that bend we create these forms:
How does this apply to the human body, well:
It may look simple, but's not and we are trained to look at objects as what we are told they are all through our young development. It's harder for our mind as we get older to say "Hey that's not a bottle it's a cylinder with ovals,etc"
But what about about those last three steps, the artist added value and light source which brings me to the next piece your piece is lacking. You have the sun coming from the left to right, but all the values are the same making your piece left.
Value is easier to understand when working just in black and white but basically it's how light or dark something is. This isn't necessarily mean that it has to do with shade and tint(darkpblack] and light[white]) when talking about hue. If you want to see the values of your piece, run it through the windows(if your using mac, uh I don't know sorry XD) photo editor, using that black and white edit. That's value, let me show you using a work by Monet:
pushing your values up or down, helps show highlights, shadows and can guide the composition of whatever you doing.
Why is value important, if you can't understand value you won't understand how light works.
Everything we see has some light source, sometimes one like sunlight or multiple ones. In realistic figure and landscape, light is critical, otherwise things will seem flat. Even if you only use line, not form, value still is in play.
So, let's look at your piece again in regards to light source and value. Where would the darkest value be on her face?
Probably along right side of her nose, near the right side of her face because the light is hitting her left side of her face, the nose is casting a shadow across her right cheek. If you look closely, you'll notice your pillow shading in piece, which is making a highlight/shadow without explanation which hurts with realism.
All these aspects(anatomy knowledge, shape recognition, line making, value, light source) will help make your drawings realistic. Of course when you throw color into the mix, your talking color theory, I think it would be good for you to leave color out when trying to attempt realism(at the moment) because you're trying to make you think is a skin tone, it's going to frustrate you by being washed out, too dark and/or generalized.
The best practice I can offer is to do studies of different body parts and the human body itself. Try going to public place like a mall or coffee shop, try drawing different body parts of people and people's general
gesture.. Keep at it, try to do it like 30 mins a day or more if you have the time, in 6 months you'll look at this and go...what was I thinking!
Just never give up, keep trying by applying knowledge you gain from others and yourself to the next piece.
I hope I was helpful.
3nodding
Links on interest and future:
Constructive Anatomy - Goes in depth about breaking the body into shapes and detail, plus it's free online!
Artistic Anatomy by Dr. Paul Richer Helps fuse art and science, it has great plates and is given to both medical and art students, showing the relationship they share.
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