Take a moment to visualize the scene and everything present in your frame.
Think about the location, the season, the weather, the lighting. Consider the colors that will be present in the surroundings (either on-location or in a studio setting), and make sure the colors you plan to add to the scene are complementary.
Carefully consider clothing options and how they will affect your photos. What focal length and aperture do you plan to use? Are there any special effects you are hoping to achieve, such as motion blur, tilt-shift, etc.?
Your imagination is your only limit, but try not to envision a scene so elaborate that it becomes overwhelming.