Perspective. A word you need to get familiar with.

All your drawings seem so empty. It's hard to understand where you try to put your attention in your drawings. There's no focus, no "golden cut". Let's take your second drawing as an example:



Supposedly it's a portrait but she's not looking at us. She's looking at something else, drawing our attention to something that isn't drawn in the picture. And again:



The dragon seems to be facing something we're not really able to see. It gives this empty feeling again as if the picture simply wasn't done.

You also need to work more with your colors. Try using darker and lighter colors to express the theme of your picture. An illustration revolving sadness would obviously. Your chibi picture's colors are so much off that it looks like some combination of a gentle halloween picture featuring a rayman character.



Smacking a black background on that and using some more "cold colors" for your chibi would have touched the theme much more than what you used there.

I'm not sure how far you are willing to go with your art but with some work it could really get much better. The opinion I've formed of your current art lies in the lines of "talented school girl"; your pieces doesn't seem too worked through.