Step 1 - Apply 2 coats of a base colour
Step 2 - Paint several irregular blob shapes in a random pattern across all nails in a contrasting colour using the tip of the brush.
Step 3 - Trace one side of the blob in a highlight colour and then a dot on the opposite side of the blob. The general advice is to use a nail art pen for this, but I was impatient and so improvised with a thin paint brush.
Step 4 - Finish with a top coat