Make a page of notes of all your ideas, make small sketches on this page rather than just spider diagrams on their own.

On a second page describe how you are going to use the ELEMENTS of art in your work. These could be Line, Tone or Colour Value (depth of COLOUR), Composition, Texture, Pattern, Harmony, Contrast, Mood, Balance etc.

On a third page make a colour sketch for the final idea; if you are not satisfied do another until you get what you are after. Make notes on these sketches to describe what you are trying to do. Any colour medium may be used, paint, mixed media etc. so long as most of it demonstrates your ideas and shows trials of the media you will use. If you are going to work in low relief or in 3D then you need to show samples and maquettes of these at this stage.