Did you know that you can draw with paint?
Using a fine line bottle as a pencil is very effective in making very fine marks on paper or canvas.
A good idea is to use acrylic paint, and make it more fluid with a binder. Liquitex Pouring Medium is a very good substitute for water, as it does not break down the integrity of the paint. Although it is more fluid, it will not become faded and washed out. Experiment with different quantities.