One of the easiest abstract techniques is using negative space. This involves leaving parts of the nail bare to create shapes, lines, and interesting patterns. Start with a neutral base color on all nails.
Then use a striping brush or thin nail art brush to paint on your design in a contrasting shade. Focus on geometric patterns like triangles, circles, diagonals, chevrons, etc. The bare nail visible between the painted lines forms the “negative space” and completes the abstract look.
Start with a nude, white, or black base which will really make the patterns pop. Use a dark color like black, navy, dark green, or burgundy for the negative space effect.