1) Use a big paint brush and make a big wash of water across the page (watercolor paper) in any shape or line. Use a watercolor or watered down acrylic paint and brush that on in the water streak. (Maybe use a smaller brush for this.) I'd recommend starting with just one color. You should now have a giant color swash on your page with some variation in the color based on where you put your paintbrush with color. Let the page dry.
2) Use a pastel (oil or chalk) and make one or two lines that loosely go in the same direction as the original color swash - or in a similar shape.
3) Use a Sharpie or other marker or pen to make parallel lines. Do not cross the color. Make your lines go all the way to the edge of the page. Do as many or as few as you like.
4) Use regular acrylic paint (not watered down) to make small marks of your choice on the page. Generally, it's a good idea to follow the direction of the original line or at least stay within a few degrees (if you move in an angle) of that direction. You could try small dots, short lines, little circles, swirls, curves, etc.