If there are slow starters, make sure they understand, but allow time to think. Many teachers use topic motivation related to student interests, experiences, and concerns. Consider student development. Consider special motivational activities to enrich their frame of reference for creative media work projects. These might be sensory exercises to make them more aware of texture, tone, hue, depth, intensity or some other visual quality being learned.
Children enjoy role playing, stories, poems, and so on.
These activities can be used to foster richness of imagery in their work. Often preliminary sketching and planning on separate paper are an excellent way for students to prepare for the main project. For many lessons it is appropriate to require some preliminary planning. It is also a chance to help them learn about quality by helping them learn ways to discern their best ideas. Many times art assignments are based on real experience the class has had.