Which practice is most important for achieving good results in watercolour?

Correct answer: Control of water and pigment

The governing concept is controlling the ratio of water to pigment. More water produces a paler, more transparent wash, while more pigment produces stronger colour and darker value; the artist must adjust this balance for each layer. Practising small washes, gradients, and repeated strokes develops reliable control. Excess water can cause blooms, a dirty brush contaminates colour, and rubbing damages the paper surface. Therefore, option A is correct.