1. Make the angle between the positive x-axis and the positive y-axis large enough.
2. Break lines. When one line passes behind another, break it to show that it doesn’t touch and that part of it is hidden.
3. Dash or omit hidden portions of lines. Don’t let the line touch the boundary of the parallelogram that represents the plane, unless the line lies in the plane.
4. Spheres: Draw the sphere first (outline and equator); draw axes, if any, later. Use line breaks and dashed lines.