If you are not the "artistic type", learning to draw might seem impossible. But it turns out that drawing is simple if you can get your brain to cooperate. A breakthrough book published in the 1980s opened the door on how anyone can do this. It is called Drawing on the Right Side of the Brain by Betty Edwards.
Her basic thesis is that the right side of your brain is able to do artistic things, but the left side of your brain is dominant and supresses it. Therefore, you need a set of exercises that push your left brain out of the way so that your right brain can do its thing (This video is a little odd, but in it an artist tries to explain the difference between left and right brain thinking and what it means to him).
Betty Edwards' book contains a number of exercises that help the process of freeing the right side of the brain. Many of Edward's techniques are now legendary and are easy to find on the web. One is called upside down drawing:
The basic idea in the upside-down drawing exercise is to take any line drawing, turn it upside down and try to copy it. What you want to do is focus on the line segments and copy them as closely as possible. How long is a line? What angle is it drawn at? Where does it begin and end on the page in absolute terms? In This video the artist describes the process he is going through to see the actual lines in the drawing.
Here is a more mechanical way of doing it, and this may help you when you are getting started. Leter you can try redoing it free-hand, without the grid, as shown in the previous video:
Another of Edwards' techniques is the vase face, as shown here - you are simply trying to copy the line on the left side as closely as possible on the right side. Again, look at the line segments and draw them as accurately as you can. Do it several times and you will get better each time:
Another technique involves training yourself to see positive and negative spaces. This video explains what positive and negative spaces are:
To create a drawing exercise for p/n spaces, take a photograph of any person and try to draw the outline of the boundary between positive and negative space in the photo. You might start by placing a thin piece of paper over the photo and simply tracing the boundary to see exactly what it looks like. Then throw that traced image away and try to do the same thing freehand from the photo onto a piece of paper without tracing.
Another exercise is called contour drawing and blind contour drawing, as explained here:
Edwards' book is outstanding and is available at any library or bookstore. There are also thousands of videos on YouTube that teach drawing techniques. The more you practice, the better you will get at freeing your right brain, and therefore the better you will get at drawing. Have fun with it!