Which preparation is most useful before starting a watercolour painting?

Correct answer: Prepare a light outline, colour plan, and materials

Before beginning, a light outline, a simple colour plan, and organised materials help the artist preserve important shapes, choose suitable colours, and work without unnecessary interruptions. Thus option A is correct. Mixing all colours creates a dull mixture, oil can interfere with the paper and watercolour absorption, and dirty water contaminates clean colours and reduces their brightness.