All the following are important things to consider for your artwork:

Composition             Important, uses the other elements of design                                       to achieve this.

Line                              Thick, thin, symbolic, realistic, emphasis.

Shape                           Arrange shapes to form composition, realistic                       or abstract.

Light and dark             Most powerful visual impact. Suggests mood,                                          time, climate, etc

Colour                          Highly expressive, indicates temperature                                         or  mood.

Movement                    Gives the picture life and energy, or                                            calmness as required!

Size                              Scale is essential to include and to get right.

Pattern                        Uses lines and shape, light and dark, and colour