This idea has worked very successfully for a number of different painters.
Paint your canvas in one colour for a background. Then create rounded rectangles or stretched circular shapes by tearing up cartridge paper. When your background is dry, position the shapes over the canvas. You can use a few or as many different shapes as you like.
Think about your colour palette as well as the composition and layout of the pieces. When you have moved the shapes around and experimented, brush over the edges of the pieces in a contrasting colour to create line around the shapes. Remove the shapes and allow to dry.
The shapes can be re-used several times so you end up with layers of line and shape over each other. You can build up successive layers using different colours to create an intricate web of lines. Experiment with filling the spaces with different colours or covering areas with washes to create an interesting work.