Hi everyone! Here's my try at animation. I'm not sure if that's clear but the character is supposed to run around with a tray screaming "hot hot hot" as if the tray was burning him. I was wondering how I could improve this piece. I spent some time trying to make the running more convincing but it still doesn't look good. Maybe the typography (and everything else) is changing too fast but I wanted to convey the feeling that he's in a big hurry. I wanted to place something on the tray but it looked bad and you couldn't tell what's that supposed to be so I removed that.

Thanks for your helpful suggestions, guys! Hopefully I put them to good use.
I reduced the number of cables and tried to fix the proportions. I also added a computer case, and some shadows.

Here are my results:

As for how to improve in general, study light and shadow around you. Pencil and sketchbook, just draw whatever catches your eye in your room or around your house, find the shadows on and around objects. Study their form. It does not have to be perfect. But with just the act of practicing you will come to learn how light works.

Thank you for this suggestion! I'll try to practice lighting more.

Thank you so much for your critique! I found it very helpful. 
I didn't realize that the shadows could be read as anti-aliasing.
Implying texture is also something I'll try to keep in mind.

I applied your critique to my work and here are the results: