Draw lots of different lines!
A line can be as simple as a straight path between two points or as complex as a spiral maze. Artists use a variety of tools to draw lines and each produces a unique result. Try using your brush to make different kinds of lines: straight, curving, zigzag, thick, thin, short and long. 

Paint a feeling.
How would you use lines to show a feeling? Look at the work of artists Joan Miró, Paul Klee or Jackson Pollock for inspiration.  Choose an emotion and paint it. Can't decide? Try anger, joy, sadness, shyness, or love. 

Paint movement.
What kinds of lines show something in motion? Try painting tree branches blowing in the wind.  What about thunderbolts flashing from the sky or rain falling on a stormy evening?

Try contour drawing.
Line drawings can surprise even the most experienced artists. That's one reason why contour drawings are a favorite warm-up exercise. You can make a contour drawing with a pen, marker or crayon.  Follow this rule: NEVER look at your paper while you are drawing. Choose an object and begin by placing your pen on the paper. Let your eyes travel slowly along the outside edge of the object. Notice and record with your pen every bump and dip on its edge. Move your pen to echo the motion of your eyes. Go slowly and don't stop until you've observed the entire length of the outline of the object. When you finish, look at your paper. Amazing! Don't you agree?
 

Now try something a little different. Start just as you did before with your pen on the paper. Let your eyes travel slowly around the edge of the object and move your pen with the same motion. This time, when you need to, check the position of your pen on the paper. Adjust it and continue drawing the outline of your object. 

Try this technique with a variety of objects. Don't worry about what your drawings look like, especially at first. Concentrate on seeing the edges and the spaces in between. Draw details and interior forms, but don't try to complete the outside contour first and then fill in. Its easier to draw one shape and then the shape next to it until you've captured the likeness of the entire object. If you practice, you will become better and better at drawing the object just as you see it! 

You can read more tips on contour drawing in Drawing on the Right Side of the Brain by Betty Edwards (Los Angeles: Jeremy P. Tarcher, Inc., 1989).

Create a wax resist painting.
Try combining drawing and painting. Use a crayon or oil pastel to make a line drawing. Then paint over the drawing with watercolor. See how the lines repel the paint. Try this with contour drawings or with designs made from letters of the alphabet or geometric shapes.