1st:Composition is the layout of all the elements in your drawing. Shape, line, color, tone, and space are all part of this.
2nd: Balance and unity are considered the hallmarks of "good" conventional art. There are some golden rules, all tried-and-tested by the great artists, that you can use to find balance in your own pieces.
3rd: Linear and aerial perspective are both important for artists. Linear perspective can be divided into 1-point, 2-point, or 3-point perspective. 1-point perspective is the simplest place to start. To use it, you just need a view and a fixed point.