Where should an easel face for best light?

The very best light for drawing or painting is light from a North facing window. If you are lucky enough to have such a window you can work in front of, your easel should sit at a 45 degree angle from the window, in such a manner that your body does not cast a shadow on your work.

That means if you are right handed the window is off your left shoulder. If you are left handed then the window is off your right shoulder.

If you do not have access to North light, then a very good light, attached over your work with a natural light bulb in it will do almost as well. Make sure it washes down across the work surface in such a manner it does not cause too much glare on the work, cast shadows or shine in your eyes