What the hell was wrong with your art teacher, man? Jeez, that's rude. Good thing she was fired, but I am pretty sure that even if you think your drawings are terrible, I'm pretty sure they are really good! Maybe you can ask your brother for art lessons? I actually once won an art show at my school for a peacock made with oil pastels. I have it hung up in my house. I have a bunch of drawings in the basement but I don't draw as much anymore. Here are some tips and rules of art for you:
1. Do construction shapes to do your base and get a basic understanding how your drawing should be constructed.
2. Always color in the same direction.
3. Use different shades of the same color for shading, but blend them instead of just pressing harder just for shading.
Hope those help, that's all I can think of/remember at the moment.