There are a lot of tutorials and guides in the net on the subject of drawing ellipses, but they — invariably to my knowledge — follow the same formula: project a square in perspective, then sketch an ellipse inside it with guides.
The ghost of Euclid cries in agony every time someone draws an ellipse like that. This guide will tell you how to do it precisely using the classic tools: a ruler, a compass, and additionally a piece of string and two pins, to render the ellipse itself.